What you are saying is that a Guest Bill has gone so high, do you have anything in your hotel policies that makes you responsible for checking guest bills and make sure it does not exceed a certain amount ? If so then you may be in trouble ..

You need to negotiate a deal with management .. your options are:
1. Not sign and face concequences
2. Sign and Face concequences
3. Resign and face concequences

I am sorry to say it is not a good position to be specially if the hotel holds your passports and thretens you ..
Good luck