RCB - Sometimes it's hard to be sure because there are so many outside influences dictating who and what we are, based on our outward appearance. We even do this to ourselves. I began transition when I was about 32. After one year of transition, I de-transitioned for a year because I still wasn't sure (I was, just reluctant to admit it). I had already changed my name, driver's license, SS info and other stuff. It was my wife who told me I needed to go back to transitioning. Thank goodness! It was the best thing I ever did for myself.
Like you I had my doubts about it. I thought I was too tall (I'm 6'), to muscular/manly, and on and on. The fact is, I was miserable and it was really when I went to a local support group meeting (at no cost) that I began to realize the truth within. I can't recommend highly enough how important a social support group is. You meet people like yourself and every shade of trans from one end of the spectrum to the other. One cool thing about this is that you begin to see where you fit in that spectrum. Maybe you can identify as more this, or more that, who knows, but it helps you find out much faster when you spend time with others. I spent some time in a crossdressing group and realized quickly on that I wasn't like them at all. Then I found another group that included both crossdressers and transgender people. It was there that I figured out where I fit in the spectrum and I also made some wonderful and life-long friends. If not for them, I am certain that I wouldn't be sitting here writing this right now.