Yes, doubts are totally normal. Everyone gets them.
I still have "WTF am I doing?" moments, and I am five months on HRT and two months full-time. I totally love being the real me and I would not go back for anything. And yet, from time to time, this voice in my head wonders if it would all be easier if I just went back to the way I was. These days, I just smack it down and carry on, since I know that that voice lies. But, yeah, we all get those moments.