If the quilting lines are supposed to wash out then don't wet it. I advise caution on ironing as well in case that sets the quilting line ink. You might have luck by pinning the whole top out flat to stretch out the lumps. If you have a large carpet, lay out the top and place straight pins every 4 - 6 inches all around the edges anchoring it to the carpet for a couple of days. If possible make a large rectangle outline of blue painter's tape on the carpet so the top stays square when you stretch it.