Hi jai-jai
Feeling nervous before something new is to be exptected. New things can feel unfamiliar and that can make us feel anxious. But remember that all familiar things began as something unfamiliar
What is it you'd like to find out before you go? Can you phone them to ask about those concerns?
You had trouble talking before but you may feel different this time and you may find talking not so hard. You can tell your therapist about your worry and your therapist will help you with this.
So, you can't know what you don't know. This is new and you will know it more as you experience it and the only way to experience it, and to know it and feel familiar with it, is to go and see what it's like.