When you tell him about it, if you just make it really clear that you did it on a whim, you're really embarrassed and you've been stressing that he'd get scared off at it all etc. etc. i think he'll find it charming. Then he'll have to reassure you, and boom he'll have to show you how much he's loving it, then he doesn't have to feel guilty and voila! Nice christmas pressie for both of you.
Option 2: say very seductively that you haven't got him a present but you did get yourself one- all u wanted for christmas was him, alone with u in a hotel... and ask if he'd oblige
Option 3: Say your parents/friend/aunt doris or whoever bought u a night in a hotel as a present and you'd like to invite him cos itll be rubbish on your own
My vote is option 1 or 3 (option 2 is probably preferable to an average guy, but a small percentage of guys may find it intimidating...)
Have fun!!xx