I exaggerated my language level, and now the conversation group expects me to help beginners

At my first conversation meetup, I said I'd studied the language for years. I had taken a short course years ago. The difference disappeared because I liked how the first version sounded.

I've attended three meetings. I can follow some familiar exchanges, but I get lost when the conversation moves away from them. People have been patient. I usually laugh when others laugh and say I'm rusty.

Now the organiser has asked whether I can sit with the beginners next time and help them practise. This is an informal social group, not a class or any kind of professional translation work. Even so, I'm not able to give the help they've pictured.

How do I correct my level without announcing that every conversation I've had there was fake? I do want to learn. The awful part is that the welcome I wanted was already available to beginners.