Well, sometimes you just can't get that perfect 1/4 inch. It matters, too, if you are using thread of different weight and you are turning over the piece. You have to be consistent

I measure a 1/4 inch from needle over and put down masking tape. Colored works best for seeing it. Then just make sure your fabric follows that 1/4 inch. Watch the tape and not the needle. I gave up on 1/ inch foot. Not as accurate.