Are your pieces machine sewn together? If so, make sure you have a good 1/4 inch seam. Test your seam line to see if the stitches are meeting in the center of the fabric and not running along one side or the other (tension problem) I like to press my seam allowances to one side. Do the thread test where you wrap the thread around both hands and pull for thread strength. Maybe ease off on the tension of your hand frame when quilting?