Plumber, unfortunately your circumstance is not unusual. I have posted here before, that before we bought our Class C, we went to several large RV shows and looked at all kinds of RVs, including Class As. We went through several Class A gassers that would have been over-weight with only the four members of our family on board, no stuff. We found similar situations with some Class C units with multiple slides and other options. These Class C units tended to be longer Cs, 30 feet or more.
While you can take a chance and use the C as is, keep in mind your legal liability if something happens and someone gets hurt or worse.
Good luck with this unfortunate circumstance.