Acceptance Cancellation

Does anybody know what are the chances of getting your acceptance revoked? Like what are the minimum requirements (particularly for U.S. highschool students) for their last semester?

I’ve had all A’s throughout my high school career except for five B’s in English courses and AP Chemistry but this last semester, despite having 95s and above in all my other APs, my BC Calculus grades have plummeted which might leave me with a C for the semester.
McGill is my first choice but I don’t want to lose my chance to go to a good American college (deadlines to accept are May) if McGill turns me away after my final transcript comes out in June.

Most seniors do start slacking off, otherwise known as “senioritis.” this is fine as long as you don’t slack off to D’s and F’s and as long as you don’t fail classes where credits are required for graduation. B’s and C’s should be fine.