Only you know the answer to that, but I will tell you that most people that are gay or even bi don't have to ask that question. They just know.
Maybe curley has a point but I wouldn't dawdel too long in this arena or exploritory thinking. Society today has a way of saying it's ok to explore but I have seen too much unhappiness from homosexuality. You are too young for all this.
Believe it or not, but about 85% of all women have had some sort of sexual contact with another woman. Wanna know how many women have had fantasies about other women? 100%. No joke. ALL women fantasize about other women. Hell, even I do it! It is completely normal to be curious. What type of sexual stuff turns you on? Pretty much anything that has to do with sex, done by a man or a woman, turns everyone on. If you were a lesbian (in my opinion), you would have said that you liked kissing a girl BETTER than kissing a guy, and you would get turned on by women all the time, not just when they're doing sexual stuff. I'm not going to tell you what you are. It's up to you to decide which relationship you like better.