Jan,
It sounds like the frame had a slight warp to it. Next time out, I'd mock it up, tape the suspension to the frame and add the wheels and tires. If it sits flat, leave it alone. If it doesn't, I'd put some water in a pan and heat to where it's just about to boil. Dunk the frame in there, wait a little bit and then take it out and tape it to something flat. Let it cool and you should have a square frame. Try it with the body on as well. If the body has a warp to it, do the same thing. If everything is square and you still have a problem, if you haven't glued the wheels on yet, take your dremel or cordless power tool and elongate the wheel's mounting hole til it sits on the ground, then epoxy or superglue the wheel in place.