In our HS, grades and teacher recommendations are only two of three factors. Standardized testing is the third. If your math grades on the standardized tests weren’t in the top 5% -10%, you would not have been moved up without a parent making a pest of him/herself (not saying this is right, but it CAN make a difference).
OP, I am curious to hear whether your parents advocated for you in this decision or were they not involved? It seems the outcome might be different if they had input.
I think your path forward is a little clearer. Math matters at MIT, and Calc BC in your senior year will be seen as par for the course.