A few comments:
– Getting a few B’s is fine. If you make any academic expereince about getting all A’s you will likely find yourself anxious and unhappy. Don’t let a teacher or professor become the sole arbiter of your success. Your goal should be to do your best work in every class.
– My S’s guidance counselor told me in no uncertain terms that admissions officers do an excellent job of only accepting students who can do the academic work required at the college. If you got in, you should expect you have the tools and ability to do the work. Go to classes, keep on top of the work, seek out help if needed etc.
– HS is about getting a broad education. In college, once you finish any general ed requirements, you should be able to major in a subject that dovetails with your academic interests and abilities.