You tell me, dude. After all, you are the world's foremost expert on your own gender--don't let other people try to tell you otherwise.
Next time that cruel voice in your head pops up saying you're just playing at it, or you aren't really a guy, think about the words it's using. Would you ever, ever say something like that to a fellow transman or a transwoman? I doubt it. You'd support them, because you know where they're coming from. Remember to support yourself, too, and give that nasty voice a kick in the ass for me. I've got a voice just like it, and every day I have to remember it's not my conscience and it doesn't know more than me, it's just a cruel little thing that makes me feel like crap, and which I have every right to ignore. Everyone has that little jerk on their shoulder trying to bring them down.
One last thing--a transman I met once said "The kind of man I am is the kind of man I am." Read that again. What it says, basically, is that you define the terms of your own manhood. If you say you are a man then you are a man. You can be any kind of man, not just the kind the media or your particular culture says is a "real" man. No one can take that away from you. They can be cruel or insensitive or just ignorant, but they can't take away that unshakeable rock inside you that says, "I am male." And if you have that, you've frankly got more than a lot of men out there, who feel like they always have to prove their manhood to everyone.