Like bixkf said, it's possible to only date/have sex with/have relationship with people who are not your gender. If you want to not "be bi", I think that's the best advice I can offer you. From everything I've hard from others and have experienced as a person who is not straight, it's basically impossible to "stop" yourself from being gay or bi. It's also really, really harmful for people to try to force it out of themselves - it leads to hating yourself at MINIMUM, and I've heard that "conversion therapy" to try to be straight can be incredibly traumatic.

I know this isn't the answer you want to hear, but I want to suggest trying to come to terms with the *fact* that you are attracted to girls. Like someone else here said, you don't have to *act* on these feelings even if you have them... but if you can bring yourself to have less internal conflict, it may be easier to live with them and maintain a "heterosexual" lifestyle if that's what you choose to do.

I hope you're able to find peace, regardless of what route you take. It's really difficult struggling with a part of yourself you feel the need to change - I've been there, myself.