@squeezy,
I think you're...
… normal.
Seriously.
Lots of people don't do well in large groups. It can feel weird and awkward to try to break into a conversation. So don't concern yourself with that.
Being the listener in a large group isn't a bad role at all. And you can pick your moments. I think you got nervous and lost your train of thought, and that happens. It's okay!
Picking your moments means you might want to make some point or another but the conversation has already moved on. But there's no law against circling back. Or just dropping your point and not even bothering to express it. That's okay, too.
Being a good conversationalist doesn't just mean speaking. It means listening, it means interacting, it means asking good questions, and it means mastering the art of the segue (you can also call it a pivot, if you prefer).
What am I talking about?
It's the art of directing the conversation to a new topic so seamlessly that it makes sense to everyone talking.
"Speaking of the Mandalorian, I heard they were making Grogu dolls in Portugal and those are going to be available for Christmas. But I'll believe that when I see it."
"Now that you mention football, I gotta say, I'm not a fan of the game but I love the Super Bowl commercials. Can you imagine being the CEO of a company with so much money to throw around that they just blow millions on a minute of advertising? I mean, couldn't they just hire a few people instead?"
"Your new diet sounds fascinating. But I'm not so sure I could eat all that pasta, week in, week out. How do you do it?"
Of course I've made up about 98% of the above, but you get the idea.
Do your best to relax, and if you want to course correct, you can do something like that. And BTW, so many people just talk, talk, talk that it can be hard to find someone who truly listens. If you do, and you ask thoughtful questions and make thoughtful statements, that impresses a lot more people than you may know.