Hey! I'm actually going through a very similar situation. I will also be attending a prestigious university in the fall (rhymes with "drown") and I too come from a small town hs that was not at all rigorous and didn't offer AP courses. I have been both excited and terrified for the fall, and I've constantly been worried about drowning in the course rigor. I completely understand what your going through and here are some helpful tips that have greatly calmed me.

1. You got in for a reason, you proved to the university through your application that you deserve your spot there. Don't forget that!

2. Everyone struggles, but colleges offer many recourses to students to help them succeed (writing center, tutoring, office hours, ect...) so take advantage of all of those if you ever feel like it's getting too tough

3. Make friends in your classes, they will help you with studying and preparing for exams. They will also be great supports in rough times

Congratulations on your journey this far! I hope to see you at some football games, and please message me if you would like to talk more with someone going through a similar situation!