to the OP: I got a good 10+ years on you, so I can safely call you a young whippersnapper.
You actually remind me of me when I got out of HS. I breezed through HS and just wanted to get college over and done with, thinking I could skate my way through. Unfortunately, I had to learn that lesson the hard way. I dropped out after 2 years. I went back three years ago to major in Biology, finished all the requirements in that three years without overloading my schedule, and graduated with honors.
My point is that you're looking for an easy way out when there is none. Dental school is going to be butt-ass HARD, and there is no way around that. The best way to prepare is to take hard science classes. Biology seems to me the best preparation. Dentistry is a science and will be built on many of the principles you would learn in biology classes. If you're going to go for it, you need to hunker down and get into it and take EACH CLASS seriously. Use them as opportunities, not obligations. Once the pieces of the puzzle start falling together, I'm sure that you'll start to enjoy your classes and want to take more of them.
I looked at the programs at UCSD, and in my opinion, Human Biology would be a good major for dental prep. The problem is, there are so many good classes listed that would be good for you to take that it would be hard to choose.
If you fulfill the requirements of that major, you will have fulfilled the requirement for over 90% of the schools out there, with the exception of those that require a second Biochemistry class.
Talk to an advisor or two, especially a pre-professional advisor. They should be able to help you and assuage some of your fears.
In the meantime, enjoy your summer but prepare to get to work in the fall. Don't be afraid to take some time off school and come back to it when you are a bit more mature.