Ava, that is all perfectly normal. I think many of us had strong self-doubts when we first came out and sought help.
There's a nasty thing called 'imposter syndrome' that seems to bite many of us. We spend time pretending to be someone in our birth gender, and fearing that we will be 'found out'. I tried to be a guy, to the extent that I took on some fairly dangerous jobs and took stupid risks; "Hey, hold my beer and see how manly I am..."
https://en.m.wikipedia.org/wiki/Impostor_syndromeWe can generalize this fear of being discovered to the point that we apply it everywhere, at home, in our professions ("What if management discovers I'm a fraud?", in spite of being a top performer...), and even to ourselves as we come out ("What if I'm really faking it? Can I pass as transgender to this doctor?")
It's just our natural uncertainty and self-awareness running a little bit amuck. As you work with your therapist, they'll help you relax a bit, and gradually learn to disclose more of your feelings to them, and even more important, to yourself.
Just give it a little time, a few more sessions. Try to be as open and honest as you can with the therapist. They are there to help you, not judge you. They can help you to find your true self.
You're doing the right thing now, by seeing the therapist. Just keep it up and find your path!
Hugs
Michelle