What is the stitch length? My suspicion is that the stitches are too small. I usually sew mine at 3 or even 3.5 mm.
Are you using a walking foot and are you going nice and slow?
Do you have all of the quilt well supported on the table or does any of it hang over and cause drag over the edges of the machine?
All of those issues can contribute to problematic stitches. Good luck.