At the moment I identify as gay. It feels so much better than identifying as bi or no label. I still check out guys out of habit. A lot of guys also have this intense energy that makes me check them out. Even though I'm not sexually or romantically attracted to them. I also tend to avoid checking out girls because I don't want to be the creepy lesbian. I'm learning to be less confused by this. But this tends to confuse other people. It doesn't help that I'm femme/non-butch looking. I also have OCD. This makes me question things way too much. I'm happy to be free from questioning my sexuality. I'm scared coming out to people will bring my OCD back.
I know how you feel. You are still valid, and this is coming from someone who isn't politically correct all the time. You are still valid even if you look at guys. I do too. Bi has never felt right. I called myself "bi" for a year, but it didn't make sense to me. I thought I was bi because I find some guys somewhat attractive, and I like the idea of penetration. But it didn't feel right. It didn't make sense, there was always something missing in that label. Then I called myself a lesbian and seriously everything made a world of more sense. Like, seriously, a lot more sense. How I felt about everything seemed to finally make sense. So I know for a fact that I am gay. But I do still check out men sometimes too. You aren't the only one. Partly out of habit, partly to test to make sure(because it never hurts to question things you know to be true, and also out of habit), and partly because yes, they can be attractive. When I look at attractive men, I acknowledge that, yes, they can look good. But that doesn't mean I want to touch them. And I don't. They are pretty but I don't like them that way. But sometimes I do like to look at them. It's different from looking at women. By the way, it is okay to check out girls if you aren't overly-obvious about it. I've noticed that straight women tend to assume that girls aren't checking them out, or assume that girls are crushing on them. So if you don't make it too obvious, they will not notice.
I think it might just be out of habit. If there's no sexual interest, it doesn't make you bi. But hey, heteronormativity can be a powerful force.