Welcome the Forum...
Ultimately this is your mistake which you have acknowledged and I commend you for owning the responsibility.
But, your story is not all that unusual and your story drives me crazy.
Dealers also have a responsibility even if it is a moral one to be more honest with their customers. This happens all the time in the RV sales industry..."Sure you can tow it, no problem."
Because your story is repeated over and over, the industry and profession as a whole has a very low trust reputation.
Sorry for your plight and good luck with it.