Hi Sophie,
I understand that feeling you are going through Hun, but believe me it is going to be okay. Your therapist will be friendly and will probably ask why you have come to see them. Just relax, take a few deep breaths, and tell them. Be open and honest with your therapist. That will serve you and them much better than if you hold back. When you do you will probably feel relief. Relief that someone else finally knows who you are and you no longer need to hide yourself from them. You may even cry during the telling and, Hun, that is okay. I've cried a bucket full in my therapist's office. They are used to it and you will feel better afterwards.
This meeting is mainly to get to know you better and to assess how they can best help you. And that is what they want to do, help you. But you will have to help them by letting them know who you are and what you need. You should trust your therapist and if you find you cannot then you should find one you can.
Calm down, deep breaths and you'll have this. You can do it.
Hugs,
Laurie