Need advice: anxious about my first social gathering in like 10 years

So there's this website(meetup.com) where you join or start a group of people with similar interests, and you just mingle and talk about you're shared interests or just whatever you want. I decided to muster the courage and go to one(my first one actually). I like anime so i joined an anime group. I figured this would be a more laid back and less stressful group to get started with. The thing is, im freaking out and getting pretty anxious because when I looked at the rsvp list to see who all is going, it turns out there are 20 people going. A small group of like 5 would be stressful enough. I don't know if I can do it. I really want to because i'm 24(about to be 25 next month) with no friends or social life, been that way since my freshman year of high school. I know I need to change, but it scares the crap out of me. This is completely foreign to me. I just don't know what to do.

I assume you enjoy anime and have things to say about it, right? All it is, is people who also enjoy anime. There may be a total of 20, but depending how the group is structured, you might not be conversing with all 20 at the same time. They could split up and discuss different animes.
Also, the more people there are, the more chance you have of finding someone you can be friends with. I'm sure you would be fine with a group of 20. It's not as daunting as it sounds

But, in the end, you will do what you will do.
How about this? Look for a smaller group and if you find one, go to that, but if you don't, you give this one a try?

I've done a couple of meetups before and usually there are more people we say they are going than people who show up. On the day of the meetup people tend to forget, or get busy doing something else, or decide they don't want to go.

Plus as Callie said, they may split into smaller groups or have guided discussions or topics. Who knows.

Oh and if you go early, there will be only one or two or three people there before you and you can start getting comfortable with them. You won't notice as much as more people arrive.

It depends on what kind of results, you are looking for. If you just want to be present there, dont worry. But if you want to build relationships, you are going to be brave and suppress the anxiety.
Only exceptional effort leads to exceptional results.