What's your situation? If you truly like these subjects, then stick with them. Don't shy away from them just because there may not be many girls in the advanced classes. High school is a whole different situation than middle school. There are fun clubs for these subjects, and you may be able to find a super female teacher who can be a mentor to you in keeping your interests going.
Adolescence is always a time of changing interests. If you are simply finding you like other subjects better than math and science, that's perfectly okay. Just don't neglect them altogether or give up on them too soon because they are challenging. No one is totally exceptional in all learning areas, but you still sound exceptional to me by taking such a serious look at your learning at your age. Have you seen the book The Gifted Kids Survival Guide: A Teen Handbook by Galbraith & DeLisle? I think you would like it.