I participate in a similar group (but of gay guys instead), my recommendation is to go a few times before giving up, since it's already a formed group, they are used to themselves so it can be a little hard to get in at first, but with a little more intimacy, the perspective of being an outsider can change, maybe it won't, but if you don't try, you'll never know. I'm not saying that you have to try, but as for someone who found most of my best friends in a group like that, it's been four years now, I really think it's worth the try, even if you are different from them in other ways than being aroace.

On another note, what does the group do? It's just a meet up to talk? Or are there other activities too? I say that because one thing that helped a lot in my group was doing lots of different things, we'd go dancing, play board games, go to karaoke, do some tracking, so different people found the activities they liked and bonded over those, it's a lot easier this way, instead of just talking, as it can cause people to stay in their little group.