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.
But he grew old, this knight so bold / And upon his heart a shadow / Fell as he found no spot on the ground / That looked like El Dorado.