Do you know that it hasn't been serviced, or is that based on not having a service record hard copy? As others have said, any MB dealer will be able to check VIN to clarify. I'd be surprised if a new one hadn't had it's first and second year services whilst under warranty, but I suppose it's possible.
The service reqts/intervals should be in the handbook, listed by engine type.
Gearbox oil change depnds what type of box you have, I think 2011 was changeover year on the cabriolets/coupés; if you have stop/start eco. system, then I think that will be the 7G+, which is a gearbox oil change at, I think, 5-years. IIRC, the earlier boxes (7G) were a one-off change at 3 years, but happy to be corrected by others.
Oil/filter and brake fluid, and possibly gearbox oil, would be my view if it hasn't been serviced. As it's out of warranty and only done 3000 miles, it would be a point for further consideration reference the gearbox oil.