it sounds exactly like your pushing them a bit with the iron instead of PRESSING them first press the seam shut on the back to one side and do all of them to the same side dark say vs the light side. NOW turn it over press down. if you push that seam with your iron too hard it will show the stitches. tada .. also once you have cut your triangles and sew them into bigger triangles you can trim those to size if well rows dont have to line up otherwise double check your cuts I guess. pressing them again stops the distortion which gives you wonky triangles. also do not use crud once you have sewn them together. ruined a lot last year doing that til the fabric was so warped. so water great before you cut once you cut it leave it be. NO STEAM. dump that water from your iron rightnow. do not use steam. groan do I know. spray starch works best when the whole block is done in my not too humble have ruined things opinion. only press no ironing. took me forever to stop doing that. ironing. i