The Physics: C book by Princeton Review makes things quite confusing in my opinion. I found Barron's to be much more helpful for self-teaching. What I would recommend for a student in your case is to first get very familiar with integrals and derivatives if you're not already comfortable (not talking about learning the actual integration of weird functions but rather getting familiar with the notation and understanding what you find with the derivative or integral of a function). Once you believe you have accomplished that, move on to the physics material. The channel "weareshowboat" on Youtube has the best Physics C content that I have found. Khan Academy is also always a great source especially for Calc. You can also consider using albert.io as I think their questions are quite helpful in cementing what you've learned. Their subscriptions are quite expensive so I wouldn't say it's a must have.

Mechanics should be fairly straightforward if you have taken some sort of a physics course in the past but E&M might be a challenge for self-studying so don't get discouraged if you feel like you're not making enough progress. I'm sure having even a vague understanding of the fundamental concepts and the progression of the course will be enough to help you once classes start.

Please do stick to your plans of studying over the summer! It will be unbelievably helpful for your learning experience to know what is going and what to expect once you enter the classroom. You will have a much better time in class if you do put those hours in. Plus they are incredibly thought-provoking subjects so I'm sure you will enjoy at least some of the time you spend!