I'd say, and I don't mean this in a bad way, that you probably won't end up majoring in what you'll think you want to major in today. It's not bad, it just means that as you get exposed to more science, you'll find that you like certain things more than others. And as for your triple major thing, I'd say it'd be overkill. You shouldn't major in a bunch of things for the sake of majoring in a bunch of things. I'm double majoring in physics and math, not cause I want to double major, but because they go hand in hand and there is a lot of overlap between the classes you have to take for them. Same with astronomy and physics. I actually know a triple major in physics math and computer science. He's probably going to stay in college for 5 years (which isn't necessarily a bad thing), but he's doing it because he's interested in all of them and they would all give him useful skills in physics. But again, there's no need to major in a bunch of stuff just to like cool. And if you're genuinely interested in all of them, I think you'll find that maybe you'll like bio a little more than physics, or vice versa and then you can just major in one of them, and then take a few classes in the other just for fun. I think you'll find that the subjects you think you're interested in are vastly different than a lot of people think they are. It's not a bad thing. I think physics is much more interesting than I thought it was 4 years ago. But just keep in mind that things are probably going to change.
As for college search, yeah don't worry about it. Knowing which colleges you are going to apply to is not going to help you at all. Basically, what you need to do is to do your best in every aspect which chickenwing and I suggested. Actually, knowing a "dream college" will probably end up just adding more stress on you and hurt you in the long run.
I also highly suggest doing summer programs. Colleges like to see that you're not just being lazy over the summer. Try to do something you're interested in though. I did a summer program once that I wasn't interested in and it was the most boring 2 months I had ever had.
I would say that, if you can handle it, you might want to try accelerating yourself a bit. Most people applying to the "best" colleges have completed at the very least AP Calculus AB, and a good portion Calculus BC. They've also usually taken all the AP versions of the usual required social sciences (World History, US History, two English, Government, Economics, etc...). I'd say you should try to get most of the AP sciences out of the way (Biology, Chemistry, Physics B, Physics C: Mechanics, Physics C:Electricity and Magnetism). You'll definitely need to ask your counselor about AP classes and try to "map out" your schedule for the next 4 years. If you can't take some of these due to not being in an accelerated math program, then try to skip a math or something. There is a credit by examination program at my high school, as well as correspondence courses with a college. But again, only if you can handle it. Don't do it just because you think you need to. Failing classes is going to look worse than not having a few of these AP tests. But also, don't be afraid to challenge yourself.
