I think I would feel more anxious of an event where I just go to a place and see if anyone likes me enough to turn up

That's self sabotage. If no one shows up its not because they [don't like you enough]. Maybe they didn't like the event you are doing irrespective of you. Maybe they have a kid's birthday party they need to attend. Maybe they're secretly caring for a chronically ill loved one. You aren't their parent or their immediate family. Don't assume you have all the info on them that would let you actually objectively conclude they didn't come because they didn't like you. In short, its not about you. They have their own lives completely separate from you.

Switch your framing. You're doing something you want to do and you are perfectly happy doing it by yourself. You want to see a particular movie. What does it matter if your friends like that movie or not? Would you skip seeing that movie if your friends said they didn't want to see it? I hope not.

In my mind a requirement for adulthood is getting comfortable in your own skin. Do the things that let you be proud of who you are and what you do. Counterintitively, its this that actually helps gaining and maintaining friendships.