"I am sorry, but the hotel is full."
Translation:Het spijt me, maar het hotel is vol.
Good question! When in doubt use "zit vol." It's generally always correct in Dutch. I've seen a couple of instances where "is vol" is used, and it's not incorrect, but less common. In this case, "Het spijt me, maar het hotel zit vol" would have been just as correct, if not better.