Why am I such a crap friend?

Today, I was gonna be going to the cinema with my friends, I was looking forward to it, but, I have no confidence when it comes to being social. Alot of the time when my friends call for me, I'll say no because I'm kinda a recluse. And so, I didn't go with my friends in the end, and now I feel I've let them down and feel like a terrible friend, I don't deserve them, they're too good for me.