Sorry to say, but doesn't sound like a defect. Are you leaving plane in sun at the field between flights, without covering the canopy? If so, that is what has caused this. The sun will heat a canopy up in no time, and shrink it just like shrinkwrap. I suggest buying another canopy, and taking an old small blanket with you to the field to cover your canopy with while plane sits in the pits between flights.