Guy's Behavior

So I got his number... Now what?

So there's this guy i think is really cute. Granted we don't talk at all, but he's in two of my classes. We usually make eye contact in class or i see him looking at me, so i took that as the green light to invite him to my friend's bonfire. Two of his best friends are going anyway, so after class when he was at his locker i talked to him and got his number. He gave it to me and said he'd see what he was doing but he was interested in going, but I don't know i feel a weird vibe. He didn't really look at me and his conversation was kinda moot. Idk. So i have his number and all i did was text him details so far. How should i start texting him. People are telling me im over thinking it and should just say hey whats up, but idk. Its like we never talk so i dont want to look all desperate. I want to seem casual and cute and not pushy. And now im totally thrown off guard with his attitude at his locker. HELP!
So I got his number... Now what?
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