I'm sorry that happened to you! I always do a test piece before beginning on my "masterpiece." Your quilt is beautiful and very much worth the effort to pick it out. This has happened to me too, therefore the lesson to do the test piece, and it is my experience that it picks out pretty easily because it's loose.
One more thing...my aunt works in a sewing machine dealer store and told me that as a rule of thumb (not set in stone but usually), you can bet that if it looks wrong on the backside, something is wrong with the upper thread and conversely, if it looks wrong on the topside, something is wrong with the bottom thread. I find this to be a good rule and true most of the time. If it's not one of those threads, change the needle! She tells me don't be so stingy with those needles, change them often! :)