A guy at work wants to take me to the club

I already said yes but I'm having regrets. As much as I would like to be one of those people who likes to go out and party and have a good time I'm just not one of those people. I was into it at one point but it was never something I actually enjoyed only reason why I said yeah is because he keeps asking I'll feel bad if I say no and he said he's bringing lots of "bitches" lol how can I say no to that. I can still say no. I just feel bad because he's a really cool guy he talks to everyone at work.