Another yeah for what Darcy said. You didn't do anything wrong and it wasn't your fault you can't automatically belt out an intermediate + ride as a beginner. Nobody in their right mind would expect you to.
Event rides are a great way to meet people and with support you don't have to worry about being left behind, though if you were able to hang anywhere close to that last ride for as long as you did you have nothing to worry about. I'm impressed. You'll learn quickly about group ride etiquette such as 'car up' 'car back', calling out and signaling crash potentials and hand signals for turning and stopping.
I know it's kind of intimidating to be new and join in but after a few rides you'll be an old hand at it too and at event rides you aren't trying to join a group who've formed a knit dynamic like the one you unfortunately ended up in, you just end up riding with the people around you.

You can do it!