<p> "... no Christians EVER worshiped three different Gods. Father / Son / Mary.... which the verse implies.</p>
'People of the Book, do not go to excess in your religion, and do not say anything about Allāh except the truth: the Messiah, Jesus, son of Mary, was nothing more than a messenger of Allāh, His word, directed to Mary, a spirit from Him. So, believe in Allāh and His messengers and do not speak of a three - stop (this), that is better for you - Allāh is only one God, He is far above having a son, everything in the heavens and earth belongs to Him and He is the best one to trust. The Messiah would never disdain to be a servant of Allāh, nor would the angels who are close to Him.' (Al-Nisa:171-172).
The 'word' directed to Mary (radi Allahu 'anha) was 'Be' ('kun'). This is the word by which Allāh (subḥānahu ūta'āla) creates all things: '….. He is the All Knowing Creator: when He wills something to be, His way is to say, ''Be'' – and it is! So glory be to Him in whose Hand lies control over all things. It is to Him that you will all be brought back.' (Ya Sin: 81-83).
The words: 'a spirit from Him' refer to Yeshua's created spirit (soul); one that was pure; free from any taint of sin or corruption – as all souls are at the moment of conception.
Al-Nisa:171-172 make it clear that Yeshua (radi Allahu 'anhu) is not divine. There is nothing in these verses to suggest that Mary is part of a trinity.
Perhaps you are confusing Al-Nisa:171-172 with these verses:
'When Allāh says: 'Jesus, son of Mary, did you say to people, ''Take me and my mother as two gods alongside God''?' he will say: ''May You be exalted! I would never say what I had no right to say - if I had said such a thing You would have known it: You know all that is within me, though I do not know what is within You, You alone have full knowledge of things unseen - I told them only what You commanded me to: ''Worship Allāh, my Lord and your Lord.'' I was a witness over them during my time among them. Ever since You took my soul, You alone have been the watcher over them: You are witness to all things and if You punish them, they are Your servants; if You forgive them, You are the Almighty, the Wise.''' (Al-Ma'ida: 16-118).
These verses are prophetic. The conversation between the Exalted and Yeshua takes place on the Day of Judgement; when the prophets – in common with everyone else – are asked give an account of their lives.
Yeshua is asked to account for the fact that certain Christians have exaggerated his spiritual station, and attributed divinity to him. Yeshua denies ever giving permission for this.
Seyyed Hossein Nasr writes:
'Jesus indicates that he bears no responsibility for such exaggerations of his or his mother's status, but rather than directly denying that he commanded his followers to take him and his mother as gods apart from God, he demonstrates an attitude of proper comportment before God by offering a response of perfect humility, saying he had no right to utter such a thing.' ('The Study Quran: A New Translation and Commentary').
Referring to Mary, Nasr writes:
'Although traditional Christian doctrine does not view Mary as a member of the Trinity, the Quran may here be referring to certain Orthodox and Roman Catholic doctrines regarding Mary, for example, her identification as Theotokos, or ''Mother of God,'' which is a doctrinal extension of the Christian belief in Christ’s divinity....the Quran may be criticizing not Christian doctrinal formulations concerning Mary, but rather popular Christian exaggerations of Mary's status that approach divinization.'
Geoffrey Parrinder writes:
'In Arabia there were in the early centuries some (called Antidicomarianites) who protested against the idea of the perpetual virginity of Mary. But there were cults, some semi-pagan, which exalted Mary in unseemly fashion. The Collyridians, an Arabian female sect of the fourth century, offered to Mary cakes of bread (collyrida), as they had done to the great earth mother in pagan times.
'Epiphanius, who opposed this heresy, said that the Trinity must be worshipped, but Mary must not be worshipped. The Qur'ān may well be directed against this heresy. It gives its support against Mariolatry, while at the same time it recognizes the importance of Mary as the vessel chosen by God for the birth of his Christ.' ('Jesus in the Qur'an - Makers of the Muslim World').
Louay Fatoohi writes:
'I should stress another important point. A common mistake in studying the Qur’an’s discussion of Christian beliefs, including the doctrine of the Trinity, is to suggest that the Qur'an talks about the New Testament only, or simply misunderstands it. The Qur'an rejects particular Christian beliefs, regardless of whether they are found in the New Testament or not. For instance, the Qur'an rejects the worship of Mary, even though Mariolatry is not a New Testament doctrine. The New Testament does not have any special scriptural value outside mainstream Christianity, which was itself defined in the first few centuries after Jesus. The Qur'an is interested in clarifying its positions on doctrines that Christians hold, regardless of the origin of those doctrines. The Messiah, son of Mary, was no other than a messenger before whom similar messengers passed away, and his mother was a saintly woman.' ('Jesus The Muslim Prophet: History Speaks of a Human Messiah Not a Divine Christ').
Concerning the Oneness of Allāh (subḥānahu ūta'āla):
Geoffrey Parrinder writes: 'The Qur’ān denies Christian heresies of Adoption, Patripassianism, and Mariolatry. But it affirms the Unity, which is at the basis of trinitarian doctrine.' ('Jesus in the Qur'an - Makers of the Muslim World').
Pinder is correct to say that the Qur'an denies notions of Adoption, Patripassianism, and Mariolatry; but he is quite wrong to suggest that it: 'affirms the Unity, which is at the basis of trinitarian doctrine.' It most certainly does not.
Louay Fatoohi writes: 'Under pressure to reconcile contradictory statements in the New Testament, Christian theologians work hard to stress that the concepts of divine oneness and unity are one and the same. The Qur'an rejects this equation, as logic does. The God of the Qur'an is one, not united." ('Jesus The Muslim Prophet: History Speaks of a Human Messiah Not a Divine Christ').
This from the Gospel of Mark:
'And one of the scribes came, and having heard them reasoning together, and perceiving that he had answered them well, asked him, Which is the first commandment of all? And Jesus answered him, The first of all the commandments is, Hear, O Israel; The Lord our God is one Lord.' (12: 28-29; KJV).
'Sh'ma Yisrael Adonai Eloheinu Adonai Eḥad'. One Lord. One God. This is tawḥīd.
'Lā ʾilāha ʾillā llāh' (There is no god but God). One Lord. One God. This, too, is tawḥīd.
The entirety of Islamic teaching rests on the principle of tawḥīd, meaning 'oneness'. This is Islam's most fundament concept: Allāh (subḥānahu ūta'āla) is One (Al-'Aḥad) and Single (Al-Wāḥid).
The word 'trinity' is just another way of saying 'tri-unity'; the unity of three persons that is said to exist within the Godhead. In the Trinitarian Godhead there is not one Lord, but three. We can see this very clearly in the following song:
'God the Father, God the Son, God the Spirit, three in one. God the Father loves me so, Gave His Word so I would know. God the Father, God the Son, God the Spirit three in one.
'Three in one and one in three, God the Son, He died for me. For my sins His blood He gave, then He rose up from the grave. Three in one and one in three, God the Son He died for me.
'Three in one and one and one in three, God the Spirit lives in me. Day by day and hour by hour- Helps me witness by His power. Three in one and one in three, God the Spirit lives in me.' (Produced for the teaching of Christian children by the CEF Press).
Search all you like, you will find nothing in the Qur'an, and nothing in the 'aḥādīth, to support the notion that Allāh (subḥānahu ūta'āla) is a trinity (three in one and one in three).
Have a nice day.