The evaporated fuel leaves a film on every surface in the boat, so you'll need to do a thorough cleaning. Take the cushions and mattresses home to air out in the sun for a few days, and then liberally apply Pure Ayre. I don't think you'll find it at WalMart, you'll probably have to purchase online. If you go to Amazon, don't buy the more expensive "Marine" version, get the cheaper "Pet" version. It's the same stuff, just labeled (and priced) differently.
Repeat as necessary until odor is gone or you grow to like it.