I see so many people going about labels and all and even if that is all true, maybe that's not what you want to hear. Too bad I can't tell you, the only one that can say that is yourself. So, I could give a few "steps"/tips:
The first is to accept yourself as you are. Meaning, you should come to understand and accept that whatever your sexuality is, it doesn't define you, it's just a part of you and it won't change anything. It has something to do with labels and all, but I see it as an exercise to deal with internalized homo-/bifobia (been there, bro, it REALLY clouds your judgement if you take a biased look towards yourself).
Second (and last) thing, go out there and do something romantic/sexual with a guy. Make out, get/give a BJ, you choose what suits you! Despite what some people say, your orientation should be defined by what you FEEL, not what you do. Otherwise we would be born assexual, not virgins! LOL And by that I mean that even if you are straight, you shouldn't be ashamed of having done something with a guy. You were curious, tried and that's that. Plus, I can guarantee that the peace of mind that comes with it is worthwhile!
Additional tips: know that bisexuality comes "in all shapes and sizes", meaning you can feel more attracted to one gender much more often than to the other. It can also be fluid, meaning that you may wake up one day not really interested in women and the next, you may be dying to be with one LOL
The last one is that old habits die hard, meaning that if you have been overanalysing stuff for too long, even after your experience with a man, you might catch yourself doubting your sexuality again. Just hold a memory of a girl who you liked/turned you on and another of a man (either if you liked him or if you did stuff and it didn't do anything to you) as "proof" of your sexuality. Use those to make yourself overanalyse things. It should go away. Anyways, I know this reply if fucking long, but if you wanna talk about it, just PM me, I'll be glad to help. Good luck