I know how you feel hun. I was terrified about my first kiss. And it was different to how I'd imagined it would be, but what I've come to realise is there's no such thing as a 'bad kisser'. It's all about how two people kiss together. It can take a little while to adjust to each others style of kissing. But once you've got it you've got it, & you just go with the flow.
The best thing is to not go into it with expectations, because then you'll just be paranoid if you're doing anything wrong, rather than enjoying the kiss. If he wants to kiss you, the chances are he really really likes you & won't just be judging you on your kissing abilities. So try your best not to think on it too much. Just think about how much you like him/ how much he likes you, see where it takes you, and have fun!

Take care hun. *Hugs*
xxxx