Definitely, relax and enjoy being young…but I don’t see any harm in healthy curiosity and the desire to be prepared…so I’ll give you a few tips.
Now that you’re in highschool, every grade counts. Do your best. Complete assignments, study hard for tests. Don’t work yourself into a frenzy over it…but do put in genuine effort. Start learning to make sacrifices for good time management and good study habits. The better your grade point average at the end of your highschool career, the more selective colleges will offer you admission. More selective schools often mean more funding (if financing your education is a concern).
The ACT and SAT tests (most colleges will want you to take one of these) have big sections devoted to English and Math. Try especially hard in these subjects. Work on reading more challenging books for fun. Try to build your vocabulary and review your grammar and composition rules. The higher your score…the more choices you’ll have.
Yes, colleges will want you to have a couple of extra curriculars. They don’t have to be sports. They can be volunteer work, a hobby you share publicly, other school clubs, drama, robotics, 4H, etc. Essentially, they’ll want to see that you have social skills, that you enjoy being with groups of people, that you can be cooperative and work collaboratively. Think of your extra curriculars as your note from home that you’re a nice person who can work in a group. You don’t have to do a million of them. In fact, concentrating on just a couple and having a long history doing them shows you can stick to something and see it through. If you end up in a leadership position, this makes you look like people respect and like you, that you’re trustworthy to get things done. If you can make your extra curricular tie into your intended major…that can help, too. Maybe you’re in the drama club and suggest an Earth Day play to educate elementary kids about conservation because you want to study ecology. It shows your drive and leadership.
Try new things. It’s a big world. Take a good look around before you choose a hard direction. And change your mind a few times, too. Best wishes!