I always say to measure four times and cut once...or was that five times? I've had my share of mishaps when cutting pieces for a quilt. I was making a quilt for my sister once, a log cabin full-size quilt. I put it together using strips, and I make all the blocks at once. That means that I cut all the fabric into the right number of strips (and there are two different widths for my log cabin blocks). Well, I ended up cutting one fabric's set of strips too narrow...all of them! When I had a bunch of fabric left over, I realized my mistake. I ended up cutting out more strips to sew to the narrow ones, so that they'd be the right width with the seam allowance, but now all my strips had a seam in the middle of them...
But my sister loved the quilt anyway. Lesson learned: no quilt will be completely free of mistakes and perfect. But more often than not, the only person who cares about those mistakes are you! Did you reverse a seam you pressed while stitching? No one will see...but it does bug me. For me, quilting has been a lesson in letting it go. I'd rather have a quilt from my grandmother with a small mistake that I can find than one that was perfect. That way, I feel like someone (an actual person) made it with love, imperfections and all!