I remember when I went to therapy a while ago (not currently in therapy at the moment), and I had a similar fear. I was nervous and anxious, but after a while the fear of trying to prove who I was went away, and we started focusing on issuing pertaining with the transition ahead.
Now that I'm moving all the way across the country to Texas, I'm going to have to find a new therapist and start the same process all over again. Hopefully, the second time around it will be a lot easier.
Anyways, be yourself and try to communicate how you feel - my original therapist was very understanding.