The first thing for you to understand is that what label you give yourself doesn’t matter. You can be bi, you can be a lesbian, you can be both, or you can just be queer-along with a myriad of other options. It doesn’t have to be the defining point of your identity, but there’s nothing wrong with it being important, and you can call yourself whatever you like and people will follow suit. Gay Lesbian and Bi-Sexual are just short labels- they can’t possibly contain the complexity and fluidity of human sexuality. Being confused about exactly where you think you fit is normal.
As to gender identity, your feelings or desire (in certain sexual situations) to be male do not necessarily mean you are transgendered. Many people/couples, regardless of orientation, fantasize or role play during sexual experiences or while pleasuring themselves. Sometimes people think of themselves as male or female because they feel they are missing out on something the way they are- a chance to be taken seriously or to be looked up to. Obviously, this is not always the case, but it can be. In the end, what you do and who you are is up to you. I recommend seeing a counselor trained in queer issues- most college and university students have one, and you can usually just show up and make an appointment. However, you can also call Kids Help Phone at 1-888-668-6868 and they will be happy to refer you to one near you.
Hang in there- you sound like a really awesome, together person, and I’m sure that you will figure out what and who you are comfortable with.