It's okay to be nervous. Gatherings can be tough to navigate!
Try to treat this gathering as an opportunity to work on your tools for OCD. Acknowledge that you will likely feel anxious while you're there, and you will likely have intrusive thoughts, and that's perfectly fine. You don't have to get rid of the anxiety or the intrusive thoughts.
While you're there, give yourself the goal of noticing how you physically feel without getting lost in the thoughts. If you feel anxious, then just make note of it: "I feel anxiety right now." And then notice what anxiety feels like, with curiosity rather than judgement.
As you feel these feelings, remind yourself that this is your body trying to protect itself. It's natural.
We are literally hard-wired to care what people think about us, because we evolved while living in small tribes. If we were outcast from our tribes, we would die. That's why social anxiety can be so strong.
But in the modern world, this alarm system is outdated. We no longer have to worry about people not liking us, because it no longer means death. Unfortunately, evolution happens very slowly, so we still FEEL like it's a life or death matter.
So you can remind yourself of this fact when you feel your anxiety: "This is the body protecting itself." It's kind of charming in a way. You can imagine your inner child, dressed up in an oversized suit of armor, taking their job of protecting you very seriously, even though they don't have to.
Personally, I would recommend not forcing yourself to stay the whole time, but also don't leave too early. Find a middle ground where you stay long enough to prove to yourself that you can handle the anxiety, while not staying so long that you ignore your own needs. Pick a time to leave by, and stick to it (unless you're having fun!). Maybe people will gossip behind your back, maybe they won't. Your thoughts will be catastrophic, and that's fine. Just brush them off with "maybe that's true, maybe it isn't."
Be kind to yourself. Step away once in a while to take a 5 minute break, maybe outside or in the bathroom. Even if you have a bad time, remind yourself that you're sharpening your tools. You're doing something that's good for you, even if it hurts.
If you can find someone at the party who you are comfortable talking to, see what happens if you're honest with them about how you're feeling: "Honestly these gatherings make me kind of nervous. I just feel a little overwhelmed."
You may be surprised to find that other people might feel the same way. And even if not, disclosing how you fee to someonel rather trying to pretend like you're having an amazing time will make things easier.
And who knows, maybe you'll even have some fun while you're there.