How to talk to strangers at parties?

I went to an event a couple of weeks ago that had about 50–70 people there. I knew no one as it was my first time at a new meetup group I joined. I’m good with starting conversation in small settings where everyone shares a common goal, like a class, but at large gatherings, I’m too scared to go up to one of the little groups because I’m thinking, Well, they’re all probably pals; I don’t want to interrupt them. Also, I never feel as though I have anything to contribute, as strange and illogical as that sounds. I put people on pedestals, even though I know that I have no reason to think myself any worse or lower than anyone else. It’s a bad habit I picked up in elementary/middle/high school from being teased a lot, I reckon, so now I’m basically the “mean girl” to myself.

There is another get-together of this group tonight, and I’m wavering on going. I’d like to go, but I’m scared I’d be just as bereft as I was last week. No one spoke to me and I left after an hour. I’m sure I was giving off some sort of “I’m scared of you” vibe that kept people away. What do I do? I’m not going to meet anyone or be able to network for jobs or be able to talk to attractive men, for example, if I can’t deal with this now.