Joined a local bike club but haven't ridden with anyone yet. Rides are by class. A,B,C,D
D is 8 to 12 mph and C is 13 - 16. I am not sure what I am.

How do I determine the class? Do I base it on the avg mph for my rides or is it the rate I ride at on flat terrain? On a long ride, say 33 miles (long for me, at least) I may average 11.5 to 12.5 but clearly I am cruising at greater speeds, 13 to 16, some of the time but the overall average is less if I have a headwind or some bridges to climb.

I don't want to ride with a group thats way better than I am so any advice will be appreciated.