Car loan

So my husband and I went to the car dealer to get our oil changed. While there we seen a truck we liked. We asked about trading in our truck for the new one. Well they took our info did a inquiring in the mean time my husband had to go to work. I stayed and they ran the info and approved us. At the time i thought we would be fine with the payment even though it was double of our current truck payment. I signed all of my end of the paperwork but my husband still has to sign all his stuff. My husband is the only one with income and I have the credit so they used us both. Can we back out? He hasn't signed and I don't see how they can force him to sign. Plus his name is on the truck which we are trading in so I don't see how they can force him. I'm wanting to back out because this truck payment would stretch us beyond what im comfortable with. I figured it all with my husbands lowest pays which he rarely gets the lowest but just to be safe. Anyways on his lowest we only have $200 extra a month and that's not including groceries or necessities. So since he didn't sign I'm gonna call and tell the dealership we don't want it. I don't see how they will approve just me with no income.