Did you mention the type of batting and whether it is thick or thin? These will also contribute to what is going on. I usually sew eith a walking foot and that helps, however even with the walking foot when I tried using polyester batting I could not get a pucker free back and it was just a doll quilt!!! I use warm and natural all cotton batting and walking foot, it is flat gives and antique appearance when laundered AND I have not had the problems your photo is showing. Iam not a long time quilter, but am an experienced sewer, (61 years and counting). You mentioned your machine is a Disney brother, those are nice machines, I had the entry level combo machine (embroidery and sewing) and the bobbin case does have a screw to adjust tension, HOWEVER it is best to leave those alone unless the machine is really screwing up. I think this is a "fabric manipulation" issue. The pressure regulation knob for presser foot on top is a good suggetion Hope this helps.:D

I am a spray baster and have had ZERO problems with puckering since discovering it. A lap sized quilt is a perfect size to start with. I have put together instructions for spray basting so PM me if you're interested. Good luck with your quilt.

I agree I would adjust my stitch length and try using a lightweight thread in you bobbin. Hope we have all been helpful. Let us know how you make out ok.

I starched and pressed a crib size quilt top and backing so stiff it was like cardboard. I had no problems basting it and machine quilting it. Of course the starch washed right out. It would be hard to starch a large size quilt that much though. I have a no baste hand quilting frame and it is the easiest way for me to get the back stretched tight enough to baste the layers together for a large quilt.

I'm fairly new at quilting but love it. Took an online course, was very helpful. Your fabric looks very stretched. That was a problem I always had. The teacher of the online course said never, never take out stitches. Practice so you don't have to. I took stitches out of my first big quilt so many times I had to stretch it a LOT to get it sewed. I should have just taken it apart and washed the top fabric and shrunk it and started again. Again the seasoned quilters can probably give you some good advice.

That one of the thingsI would also recommend. Some great advice here on making sure the back is taut. As someone else make a test sandwich to work out some of your problems. Good luck and don't give up. Just walk away for a short time if you have trouble.

Are you lowering your feed dogs? Also, I agree with the others responding to your question.

A walking foot helps to prevent the bottom fabric from puckering. When I quilt I pin each row as I go besides the all over pinning. I usually do free motion quilting using a darning foot and feed dogs down. works good for me.
Also the quilting spray helps to hold the quilt in place but I still use lots of pins and also if basted with thread....

The problem I think may be your tension. I read an article on this very thing and there are two area's where you adjust your tension. One is quite visible on the machine. the other is a little knob on the top. The one on the top will relieve the tension on the pressure foot. Mine, I use a screw driver to turn that knob...Hope this helps..and continue to use your walking foot with feed dogs down.

When I machine quilt I use longer stitch length and go slow. I also check progress along the way. Good luck!