I can't see your contract so I have no idea whether you can back out or not but do have some thoughts.
Six % on an old RV seems absurd to me. A mortgage is over 4% currently and an RV is financed at more like credit card rates than mortgage rates. The rate quoted sounds reasonable for an old RV.
If the interest rate is that big of an issue I don't think you should be buying an RV. Save up some money, pay cash for something cheaper that you can afford. Owning and maintaining any RV is very expensive. The payments on a loan are only the beginning of your expenses.
