Please alleviate my worries--will I get rescinded?

Applied ED to top 15 school. Will make 2 As, 4 Bs, 2 Cs in all AP/IB courses. Very rigorous course load, extracurricular load.

Will I have to explain my grades? Should I contact the admissions office or not mention it until it’s an issue? My GC is useless.

I think you should be fine; colleges really dont like to rescind acceptances unless a student is doing very badly academically (As in failing a class/lots of Cs and Ds) or if they have a disciplinary issue. Don’t worry!

It depends on the school. According to the William and Mary admission’s team they will send a stern warning letter asking for an explanation when students have 2 C’s, 1 D, or an F. (http://wmblogs.wm.edu/admiss/you-cant-spell-calculus-without-2-cs/) They also say that they prefer you to contact them before rather than the other way around.