I use mini binder clips to "pin" the seam matches when paper piecing. I find that is easier than stabbing one side with a pin, then trying to get it perfect on the other side. If you put the clip with the edge exactly on the seam line, then you can flip the units open & check. If it's right, put a pin on each side of binder clip. If not, open clip and slide over. Check and slide until it's right.