Personally I think that is quiet natural to have moments of doubt on many levels when you chooe this path. After realising or having decided that is who you truely are, you may go through a great emotional shift that you have unlikely experienced before or ever will again.
I assume that arriving at that point is not one made lightly and often after many years of self exploration, re your identity, attempting to resolve inner conflict. The later a result of being raised and educated in a gender orientated way that does not sit well with your inner self. Social stigma, media, family etc., can all contribute to keeping you in that place longer than desirable. Hence we can find ourselves later in life feeling we have been trapped inside oursleves. Possibly causing all kinds if issues and truama throughout our lives
I reached a point in my life when I just knew that it was a path that I had to take. However, that did not prevent me from having thoughts of self doubt on many levels. But my committment and self need were much stronger than my doubts. The doubts I had were short lived, the more my life continued those ideas never surfaced again. It can takes different things for each of us to be able to discover our true self.
Mine was just learning to love myself and be able to accept who and what I was. It sounds so simple when I read that back, but it took me almost a lifetime to discover it.
In my heart, I know now who I am and who I have been all my life.
I hope you can find that too.