I think it helps going into it with the mindset, "they're here to help me and everything that is said is private and kept between us." That's what I went in with at least. Idk I think I'm weird, but I never had any problems at all going into the meetings and talking about any and everything, and that is totally the opposite of how I always am; I keep everything personal to myself. I had more difficultly making the call and the appointment than I did with the first few meetings.....That's way more scarier to me at least and you've already cleared that hurdle!
The first meeting will prolly just be about getting to know each other a bit and getting some background, why you're there, problems you're having, what your hoping to achieve by going, growing up history etc, prolly nothing too in depth; that doesn't sound too scary right?!?!
But ya, as others have said, just be as honest as you can be, it can't do you any good to lie about things there. I know I never lied to mine but there were a few "big" things I "forgot" to mention

, well not really but wasn't comfortable mentioning it at the time, and hey, it's easy to get distracted and 45-60 minutes goes by really fast sometimes...!!!! If there's something you're uncomfortable talking about or something comes up that is scary or something, ask to put it off, talk about it later, until you feel ready to talk about it, until it "feels like the right time".
If, after a few meetings, you don't like this one or don't connect or don't think they can help, then don't give up, look for another, one who's better for you, because unless you're in the middle of nowhere, there's prolly a bunch nearby to choose from who could potentially help or be better.
But ya, I definitely love going, feels good to be free and be able to talk about stuff. Hope you have a good appt. and everything works out ok for you. Let us know tomorrow, k!