There are many students with straight A's and 1600 SAT's who are not accepted. The application is a "total package." Many important parts, like EC's, Sports, Community Service, Leadership positions, summer activities, physical fitness, medical, on and on. So don't worry about B's in AP classes for sure. All you can do is do your best. If you have done your best, don't worry about anything. But everyone should have a Plan B, C, D and E.