I feel your pain as well. Luckily you found it before you quilted it. I was looking at pictures of my GN quilt which was already completed and mailed to her when I discovered in the picture one of the blocks in the Ohio block was insert wrong, talk about GRRRRRRRRR! I checked the quilt over so many times and never saw the error. At least you can correct it before it is done. Good Luck :-)