Maybe you are reacting to the change in your life. If you're used to always dealing with your problems alone and your parents and family haven't been there to help, and you may have borderline, you are probably feeling a 'split' inside yourself. On one side you really want help, to open up, to feel understood, something you never experienced before, but on the other side you are so afraid that it won't happen, expect it not to, want to push away and just hide and stay the way you always did.
It's so brave of you to have taken the step to recovery and that in itself really proves that all you want is a hand to reach out to you and help you. You are afraid of opening up to someone and have it all thrown back in your face and that is very understandable.
When you get to the therapist sessions, take it slow. Open up as much as you feel comfortable with, tell your therapist this is uncomfortable and you have never done this before and just do it step by step. Don't pressure yourself. Answer the things you feel comfortable with and save whatever questions your therapist has for a later time when you have more trust in that person.
Being diagnosed with a personality disorder is going to help you find out who you are and why you feel the way you feel. It sounds a lot like to me that what you are going through right now is identity confusion and I get that a lot myself during changes and when new things are introduced in my life. They are unknown and therefore intimidating and frightening.
Take your time and know that things are not getting worse because you are reacting to them, but that it is your personality disorder coming into play. It isn't you, it is something else that is alien inside of you. I really wish you luck with your therapy.