I've done things similar to this before; in fact I just did it on a table runner yesterday--lots smaller to take out than a quilt! I always blame myself for not paying close attention when I get in the "thrill of the moment". I think this is why someone coined the phrase "Measure twice, cut once" When these things happen, even though I'm HUGELY frustrated, I try to take a deep breath, get a cup of tea and calmly rip it out, and then I complain bitterly to my quilting buddy!