1/4" seams can be a pain in the ........ (you fill in the blank) The biggest question ~ do you have a 1/4" foot? Trying to sew, just using the itty bitty, tiny little mark on you machine is another pain in the ....... You should be 'guiding' the fabric, not push, pulling, or stretching.
Rotary cutting does also affect the outcome of your blocks. As does pressing and your 1/4" seams.
Try to use the same brand of ruler on a project.