How can I stop being so nervous about kissing this girl?

I met this really cool girl a few weeks ago, and we've been hanging out and talking online, blah blah blah, all the usual stuff. Last week we went to a park and I was hoping to kiss her when we had some privacy. I managed to sit down next to her at a picnic table and put my arm around her before I got incredibly nervous. It took literally an hour of holding her hand and joking around before she finally kissed me first, and then I was able to kiss her back and then lean in and go for it on my own (a first for me, actually, despite having kissed two other people). So the evening ended well but I was so embarrassed the next morning because I KNOW I acted like a child, but at the time I couldn't help it.

I saw her again last night and I figured I couldn't possibly be so nervous again since I'd already kissed her. But it was even worse! I chickened out several times when I was going to try. Finally she walked me out to my car and we stood there for another five minutes or so until I finally went for it just because I felt bad at making her wait so long.

When I was driving home I was really upset, because I felt like something was wrong with me. I wanted to kiss her and I knew for sure that she wanted me to, but I just felt so paralyzed. I do have some anxiety with people in general and I think that's part of the problem, but I like this girl and don't want to be so scared of something that I actually enjoy once I get up the nerve to begin. I already told her that I was exceptionally nervous but all she did was wait, so what could I do to make myself less scared?