Logically hot water will,shrink cotton fibers...did you prewash fabric? If so, it is already shrunken, but maybe a good steam ironing will do a bit more. Do you know what seams are not true 1/4" causing the puckering? Can you just redo those to adjust. Maybe stitches were too tight in that area causing the puckering, again redo changing stitch length or tension....just a few other ideas for you to,think about.