I struggled with feelings like that back when I transitioned, oh yes.
It takes a while for that "voice" to quiet the f down. Me, I think that voice is actually a manifestation of dysphoria -- a response to the pre-verbal feelings of sadness, anger, fear, and disgust that combine so uniquely to become dysphoria. Well, then the mind tries to process those feelings, and it identifies the current changes in one's life (transitional steps) as the cause -- which makes sense, actually, because when we transition it really does open us up to so much dysphoria that's been more or less effectively repressed before now.
And as we transition, we become much more keenly aware of what it will take (both bodily changes and social ones) to get properly gendered by ourselves and others day in and day out. That "self critique" will definitely feed the voice of doubt.
But the thing to remember, always -- how do you feel about being gendered one way versus the other way. Not about the possibility, or what it will take, or what it will cost, but just the feeling of being properly gendered rather than wrongly gendered. That's what really helped me to know that I was on the right path. Because those feelings never changed -- the wrong gendering made me angry, and upset, and hopeless, and despairing, and full of loathing. The right gendering, on the other hand, always made me feel relieved if not euphoric.
Go with those feelings.