I have done this before but not had the problem you are having. I can't remember what paints I have, but think they are basically the same. Did you maybe squeeze the tube a little too hard on that particular line? Sometimes the tube puts out too much "paint" and it will cause it to run. I paint a little on a scrap before trying on the real pattern. About the only thing you can do when this happens it to try to remove it with a toothpick or draw over the line to make it look more pronounced and then do the same on the other side so it matches. Sorry it happened.