I have put blocks in the quilt wrong and didn't realize it until it was quilted. So they are still there. But the one that bugs me the most is in my DH quilt. I made a Tennessee Waltz quilt in the setting where the snowball block is very prominent(s?) the fabric between the stars arms was supposed to be a lighter shade of the color of the star. Mine was too dark and the stars do not show up! The quilt is still pretty, but it would've been striking if done correctly. So now I either make up a sample block and/or take a picture with my camera to help with the visual aspect.