You're not overreacting. It's quite normal to be anxious when you think about exposing this part of you to a stranger for the first time.
It's a big step, and exhausting. Take care of yourself and be aware of your anxiety. Don't deny it, but don't let it control you, either. Remember to breathe.
I just saw a new "T" today too, but he's not my first. I remember my first session with my first T was tough, but the talking comes easier with time.
Think about it like you're opening the door to let the fresh air inside.
Stay strong, brother. We're here with you.
"There is a Catskill eagle in some souls that can alike dive down into the blackest gorges, and soar out of them again and become invisible in the sunny spaces... even in his lowest swoop the mountain eagle is still higher than other birds upon the plain, even though they soar." -- from Moby-Dick