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