Anxiety and new people?!?

Today, I sat down for lunch in the university cafeteria, being my usual, antisocial self watching videos on Facebook when this cute guy kinda just came and sat down and smiled at me and started talking to me. It's pretty unusual for me to be approached by people so I was a bit nervous, but I sat through it and smiled and nodded at everything he said and he was really quite interesting. Then, as he was leaving, I think I kind of blundered.

He asked for my number and I obliged, thinking it would be nice to have a new friend in university since I don't really know that many people outside my usual circle of friends. That was all fine and dandy, but then I asked him what brought him to sit next to me, and he said it was because he thought I was cute.

Getting compliments from strangers is equally unusual for me and being the awkward, antisocial geek that I am, I just said "Aw, thanks!" and I didn't compliment him back and it's been bothering me since because he kind of looked disappointed and that's causing me anxiety over how I behaved and responded.

It doesn't help that I now realize he was probably discreetly flirting with me, and I'm an ace of spades. If he ever messages me, he might realize that I'm not going to engage romantically with him and that might shut down any potential friendship and that kinda just… it makes me feel wrong, I guess.