What comes to mind is maybe you are inadvertently pulling on the quilt? Or maybe the walking foot is defective. Have you made a practice block to see if your stiches are normal? If not, I would do that. It might just be the tension gets too tight on the big quilt. Also, try retreating your machine and even change your needle to one with a bigger eye. Do one thing at a time to see what works. Good luck. Gina