Did you let the batting relax before you did the sandwich? Also I have found that if I keep the fabric taut from side to side as I stitch it seems to prevent wrinkles ahead of the pressure foot. I do use a walking foot but sometimes wonder if it is broken. I use the red finger tip covers so I get a better grip on the quilt as I go. Also, make sure you have room in the back of the machine so the quilt can keep going out the back. I was rolling the part of the quilt under the arm and it was so stiff it couldn't fall behind the machine. And keep the front bunched in your lap so the machine does not have to pull so hard to get it through. If you are stitching on the bias, you may be stretching it in that area.