I agree that it would be easier to answer if the question was shown in addition to being described. It isn't clear where the sashing is off - in relation to the points or in length or what?
As to the other quilts being "perfect" - NOT (and I am speaking from personal experience). All of my quilts have some little issue or other. The good news is that small discrepancies often do not show up as glaring errors. I give myself a 3x order and if the problem still persists after 2 attempts to get it right, the 3rd attempt will go in the quilt as is. Most of the time when the quilt is done, I have a tough time finding the problem bit.
So don't fret - perfection is dang near impossible.