Probably down to nerves, but you should know that not all girls get amazingly wet.
I think what you really need to do before you try again is communicate. Talk to her about your nerves, about what each of you likes, about what you both want and expect. If you find it hard to talk to the person you're going to be having sex with, you need to ask yourself whether you should really be having sex with her.
Its your first time full stop. I find it a good thing to not have big expectations with your first time with ANY new person. The first few times with someone should be about getting to know each others bodies, getting comfortable, becoming familiar and communicating what works for each of you.