when doing the small blocks like that I had the same problem. My teacher said the line on the ruler went right on the line to cut or edge of fabric. She checked my seam allowances and said they were accurate. She suggested me to use Aurifil, it is 2 ply ver 3ply. I couldn't believe the difference this one extra ply meant. My blocks were accurate. I also try to do scant instead of full 1/4 in. Scant is just one needle width over which isn't much but like the one less ply adds up when you have lots of seams going across a block