Grades

If I got a B in PreCalculus, but then got an A in Calculus AB AP and Calculus BC AP, would that B make a difference in my chances for Columbia?

Does an A in Calc "make up’ for a B in precalc? No.

If you get rejected, will it because of one B? Also no.

It’s nothing to stress over. Chances are lousy for everyone, because no matter how perfect your stats are, it’s still a hyper-competitive reach school. Also, culture is a big factor in the decision, not to mention affordability. Make sure you have a good list of reaches, matches, and safety schools. I would also consider scholarships. They’re a much better deal.