Stretching it will ruin the quality. It's at an almost 16:9 ratio now, stretching it wider will warp the image if you don't increase the height. The height unfortunately is the max the forum allows for a sig.
It's a simple image though, so I can reorganise the text on the image for you. Or, if you have the image without text I can add it in and keep a 'longer' image for you.