Just go in there and play your ass off!
If you practice the rock songs enough on the DB before you get in there, you'll be fine, especially if you have 20+ years on EB.
If you tell them "I'm...uh...n-not so good at this big cello thingy..." they're not going to take you as seriously. You'll be fine, just practice as much as you can to learn the DB before you get in there, and have fun

Good luck and tell us how it goes!