Take your time, chances are if it's a first shot at this it'll be a chat about expectation and realistic outcomes.
I don't like the following but it's the honest way to say it, I've been through plenty of courses of counselling and I always treated the first session similar to the first round of a boxing match, its an opportunity to get a feel of the other person there, obviously there's no winner or judge or outcome or world titles on the line. I raise this this way because sometimes you are and sometimes you are not comfortable with the counsellor you get allocated. I've had good counsellors, less good ones, and brilliant ones. One size doesn't fit all. All's you can be is honest with them and importantly yourself.
It took time to get to this point, it took time to look for help and improvement, it'll take time to unburden yourself of what ever it is that's weighing you down. Nice and relaxed and calm and clear. You'll be fine.