Is college hard? And if so give me pointers plz!?!?!?

Ok I am freaking out about college. I want my major to be in marine biology, a lot of hands-on learning, but I don't know if college is going to be quite as difficult as everyone says. I took an ap US history class and it was ridiculous; however, the teacher was a big b$&@�! She told me I can't go to college and always accused me of cheating. And I am an honor roll student and have a 3.8 gpa. But in the end I got a B in that class. I also took AP biology and got a 102 in there. Because I love science. I have like 7 science class credits when we only need 3. Can someone please tell me how hard college will be for me? Thanks!