Why do I get anxious with girls?

There's this girl I know and went on a date with once, her and I didn't really click...but i'm more the type of guy who befriends a girl first and then feelings sometimes follow. I'm not the just go on a date and be in a relationship after 2 dates kind of guy. but anyways this girl texted me today and wants me to go to a kickback with her tomorrow and we could "go together" except I hardly even know her, and i am getting the impression she wants a relationship right away. I get so anxious when put in these types of situations. what do I do! we are 19 and i'd rather me actually know this chick before going to a party with her otherwise it's just awkward because i know no one, and i hardly even know her. is this normal at all?