Answer:  Consider how strange college would be if you could only sign up for courses that you've already had! Of course calculus is not a prerequisite for calculus. You may feel that since some of your classmates have had calculus before that they have a huge advantage over you, but in fact, having calculus in high school is only advantageous if you had a really good course, learned a little of the material, but still realize that there is much you don't know. If any of these conditions haven't been met, it is probably better that you didn't have AP calculus.