If you starch the top and bottom heavily before sandwiching, that would do a world of good. If you can't take the quilt sandwich apart, even just spray starching both sides several times should help.
I also recommend lengthening your stitch (try 4). Sorry, I may have missed this, but are you using a walking foot?
A thin cotton batting is easier to machine quilt than a polyester batting.
Also, looking at your photo, it appears that you are quilting along the bias. Fabric that is not starched will distort more when you are quilting on the bias, so this may be contributing to the problem. Honestly, I think starch would solve a lot of your problem.