I know what you are talking about, I have had the same issues. I am careful with my cutting and happy with it. Thought I was doing a 1/4 inch seam, but when I put the darn thing together it was small, I was to end up with a 16 inch square, but it was not. So, I started to sew with a scant 1/4 inch and make sure the fabric is going through the machine, it is going straight, especially at the end. You would be surprised how many times I check and it veers off one way or the other. And that is a pain when you go to piece this block together. It is not the right size. I have had more luck with accuracy doing both of these things. Good luck, it is frustrating, I have a lot of...what the heck? moments.