Well since the Passat is rated from 25 to 31, depending on engine and model, and you did not note what model you have, you may be right there.
I might also note that at 2K it is not totally broken in yet so it is hard to say if it may improve. Most of my cars improve to about 50,000 miles where they level off.
Your driving style makes a great difference in the mileage.
So I don't think we can make much of the mileage.
As for the roughness, I have not noticed any current VW being rough.
The real answer to your question however is at the dealer. You have a warrantee, and they take car of things like low mileage and rough engines for free, and they are the experts. At least the should be.