I think there are multiple intelligence:

http://skyview.vansd.org/lschmidt/Pr...telligence.htm

and because you are really good in one area does not mean you are good in others. Intelligence is a bit of an aptitude and school work is mostly just interest/applying one's self and literal learning how to do things in a way our teacher's/parents want. It sounds like you figured out what you wanted though and were able to learn what you want to learn for yourself, that's great! Keep working on what you want to work on.