I've found after a couple rips, the fabric has stretched a little. I just figured out where my mistake is on the quilt I am working on and it showed (mine was dark blue and a white intersection that was off by more than 1/8 inch). After a lot of remeasuring I finally figured out my problem wasn't the sashing I just put on but the square itself. Now its is off less than 1/8 inch and I'm going to have to let it go.
I've learned a lesson today: Measure before you rip because what you think is the problem might not be the issue.
I took that darn sashing strip off twice.