By " bunching up", do you mean it's gathering up the quilt, or nesting threads beneath? I take it you have your walking foot on for this , and a proper quilting or topstitch needle for the thickness of thread you're using. So perhaps the tension is too tight...loosen it it tiny increments on a practice sandwich made with similar fabric & same batting as your project. And l agree with Tartan, if your machine allows, lessen pressure on the foot.