Slightly longer barrel than what you wanted....
Most people don't have issues with the length of the barrel--usually it is the size (length) of the grip and the thickness of the gun that decides whether the gun is more comfortable than another. Since you are looking at the same gun with different barrels, it really shouldn't make a huge difference in terms of concealed carry.
I doubt you will have any trouble carrying with a Supertuck either, and with practice, practice, practice you won't even notice that your gun is 1/2" longer in the barrel.
But, you must ask yourself this: why did I pick the Carry Elite Dark in the first place? Were the reasons for picking it important enough to hold out for the correct item?
IF you do decide to keep the gun, you should request some kind of discount. After all, it is NOT the gun that you ordered and responsibility for the mistake rests wholly on the clerk that ordered it for you.