I have been hand embroidering on the butterfly quilt blocks for all most a year. Finally got done and when I went to look at all my blocks. One of the first ones I did has a yellow stain on it. Now none of the others have a stain. Just that one. How can I remove the stain? It looks like some one peed on it. It don't smell, not greasy, about the size of a half dollar. I am just livid. What can I do?