It's natural to be scared. This is a huge, huge thing you're contemplating and it has so many perils. Life would be so much easier, in so many ways if we could just stay as we are and somehow wish the whole thing away. And for some of us, that denial enables us to continue living a male role for years, even decades. But in the end, we have to accept that we are who we are, and deal with all the consequences of that acceptance. Having waited far too long, I can only say that (a) you have my absolute sympathy because I know just what that fear and uncertainty feels like (particularly if, like me, you can play the role of being a guy well enough to fool the outside world, and even fool yourself some of the time) and (b) you will know in your heart whether you were made to be a woman. So listen to what your heart tells you. Trust it. Trust your emotions. And then do what feels most true to you.
'To thine own self be true.' Because a false life is no life at all.
And yes, as the other girls have said, the process of arriving at your own truth is made a thousand times easier if you have an experienced, sympathetic therapist to talk to. Transition is the most absolute change that anyone can make in their lives. It's not to be done lightly. But it's not to be denied, either ... IF it's the right thing for you.