Are AP classes really structured after college classes?

Not entirely.

I will say that they are closer to college level courses (in terms of course content and complexity) than ordinary classes however what happens is that, in order to compensate for this increased difficulty they have a very relaxed grading structure.

For example in AP Calc BC, if you get 60% of the questions right (usually, sometimes the grading scale varies) then you get a 5. Whereas in college courses you will be graded out of a 100 and not just in one final exam but rather with a series of continuous assessment. You will have quizzes, papers, projects, presentations, homework and/or exams.

So while AP courses may give you a taste of what college courses are like, college courses will certainly be more difficult (at least at Brown), but if you get into a college then be rest assured that you can thrive there, else they wouldn't have admitted you.