For about a week I have been trying to get someone to point me to where Catholic Mariology contradicts scripture. I got plenty on how it contradicts various Protestant theological fantasies, but I did not get an answer. May be you can try?
1. Mary was conceived of a virgin. The Bible indicates only Jesus was born perfect and sinless. Catholics want to extend Mary to being perfect and sinless, which in my view diminishes the miracle of Christ.
2. Mary remained a perpetual virgin. Reading the Bible one would conclude Mary and Joseph were married and they had other children. If they were not married, why is Joseph referred to as Jesus's father? Without marriage, Joseph would have no relation to Jesus. And trying to blow off all the references to Jesus brothers and sisters as just being cousins or friends is pretty far-fetched.
3. Other things such as the assumption of Mary or Mary being the co-redeemer is completely made up. The co-redeemer talk in my opinion is blasphemy.
4. Mother of God/Heaven vs. Mother of Jesus. In my view, Mother of God and other titles Catholics want to put on Mary, implies much more than what is in the Bible. Using the concept of trinity does not mean the terms God and Jesus are completely interchangeable. When you do, it establishes conflict.
I am sure you can post pages and pages that 'explains' these and other issues concerning Marian doctrine, but in my view it is only rationalization and falls way short of proof.