You are too hung up on labels and trying to fit in, when you don't even know who you are yet.
Bisexuality implies a sexual attraction to both sexes. Based on your posting, it doesn't sound like that's where you are.
You might be attracted to both boys and girls, but I question whether you are old enough to understand sexual attraction.
You might feel more comfortable around this group, because you aren't expected to behave a certain way (sexually) and as long as you are 'in the closet' you are merely an observer, and not a participant.
Join the group as an "ally" (friend) and hang around. Get to know the people and interact with them.
Gays and lesbians have no gender confusion, they are proud of being boys and girls and don't want to be anything else. A lesbian is a girl who is sexually attracted to other girls (although in high school, that might be loosely interpretted).
There's nothing wrong with having gay and lesbian friends, and sometimes it takes a few years of living and socializing among them to figure out if that's where you belong.
Instead of being 'in the closet,' just be yourself, and become a friend. It's clear from this post that you have no idea what your sexuality is, or what sexual orientation is all about.
Hang with kids your age, whether gay, straight, lesbian, etc .... when you have found a "fit," you'll know, it ... instantly. It will be a very comfortable and unstressful feeling. When you figure out what makes you feel that way, you'll know where you fit, and there's no need to "come out" because you aren't in any closet.