Before quilting this panel I ironed it and thought that I had removed the crease in the center where it had been folded in storage. However when I photographed in bright light outside (after quilting) the crease reappeared.
I know you are not supposed to iron quilts but the crease was really obvious when hanging. So firstly I steamed the crease. This softened it a bit but it was still obvious. So I wet the area and ironed it - much better.
I must add i use Nu-wool wadding that is 60% wool and 40%polyester. I am not sure that this would work with other types of wadding.