You shouldn't be nervous. A training run with the CCG is like playing friends you simply haven't met before.

I am planning on attending this Saturdays run.
I attend as many of these runs as I can, they are a lot of fun and from a teaching stand point they are incredibly rewarding. I have been MIA quite a bit recently but these training runs always encourage me to come back.
I don't know if anyone else in the group is confident enough in their abilities to teach stunning, but I think a successful training run would need 2 teachers, one in front and another behind.