I had a very close friend in high school, a girl, who had 'crushes' on other girls. She would follow them around, she'd draw pictures of them (she was an artist), she would talk about them incessantly. But she wasn't a lesbian, and I know that for sure because we are all grown up now and she got married and had kids and became very religious.
Nobody, boy or girl, is 100% straight. We -all- have some gay tendencies whether we like to admit it or not, even to ourselves. And, well, being a guy I can understand how girls are attracted to girls, because I'm attracted to them myself! I think girls are wonderful and beautiful and what's not to like? 8^)
Anyway, you are in that time of life when a person grows very quickly. By the time you are 18 you'll be a completely different person. Your feelings about things are changing so quickly that it can get really confusing. Your body is still sorting out the hormone situation. Middle school age is one of the hardest ages to be. So just relax and try to get through it, and see how you turn out in a few years.
In the meanwhile, there's nothing really wrong with being lesbian or bisexual. We are more accepting of gay people every day, and by the time you are actually able to -do- something about it, it will be even more acceptable. Just relax and listen to your body.
Good luck!