Goals you set should depend on what you want. It sounds like the main things you want are to do well in school and get good with girls, so start there.
School - First, ask why you're doing this. If you're like 99% of other people, you're trying hard in HS to get into a good university. So make that your goal, and remember that whenever you don't feel like doing anything.
As for specific goals, focus on what you can do right now, tomorrow and the next day. The biggest problem with goal setting is that it's some vague thing far in the future. What can you do NOW to move you along your way? What can you do tomorrow?
Girls - I have a hard time believing you really have no extra time. You get off school at what, 2:30? You're not spending 12 hours studying unless you're really wasting your time. Focus on the important stuff and don't do more than you have to.
So when it comes to girls, you just need as much experience as possible. Set aside as much time as you can to either socialize with girls, or go somewhere that you can approach. Remember it takes tons of experience to really get good, but you're starting early, so if you don't give up you'll be fine.
Same day by day rule applies. Eventual goal: Hot girlfriend or new girls every week, whatever you want. Goals now: get as much experience with women as humanly possible.