Fear and doubt around completely switching over seems normal to me. I've been on hormones for years but still haven't gone full time so the wanting to and not being able to yet (easing my kids into this for the past few months) has created a wee bit of mental stress.
I often ask myself, "Am I really doing this? Do I really need and want to do this?"
For me the answer is yes but to get there I have to try and envision what it would be like to be woman. Like you, that gives me peace and makes me very happy. When I think of going back to full time male I am very much not happy.
So what I mean to say is I think that living in the middle is real hard and creates it's own doubt and perhaps since you are in transition that this may be a factor.
Sounds like you are working it out though Sophie which is awesome.