Did I **** up my chances for a good college?

Amherst is the Harvard of liberal arts colleges. They turn away straight A students. You don't have a shot at them. In fact, if you're getting mostly C's, you don't have a shot at any 4-year college or university, and you probably shouldn't be considering going to college at all. A C average is failing in college, and college classes are a lot more demanding than high school. Either put in the necessary work to raise your grades up to mostly A's this year so you'd have a shot at some schools (but not top liberal arts schools), or come up with a different plan for your future.