I made a DWR for my nephew's wedding and the instructions that I had included spray starching everything. Obviously you do not need to do this for paper piecing the arcs but if you starch the melon pieces and sewing with the melons on bottom and use a stiletto to ease the arcs into place it should be easier. Also I noticed that you do not have your corner pieces sewn on. The instructions for the DWR that I had called for sewing on the corner pieces to the ends of the arcs before sewing on to the melon pieces. Then of course pressing the piece will help as well and pressing so that the melon piece remains flat. This means pressing to the arc not to the melon. With a little instruction from me my DSD helped me press the blocks and there was not a pucker problem at all. Good luck. We all want to see the finished quilt.