I want to have an edge around my design on my scarves, but try as I might, I do not have a steady enough hand and the line I draw with gutta looks terrible. Any suggestions?

It does help to have your wrist resting on a solid edge when drawing with gutta and to always draw towards yourself. However, if you cannot do this, why not try using a stronger, darker colour around the edge; then when you add salt it will help create an organic border; which can often look better than a hard edge border anyway. I used to do drawn borders, but now only use organic ones.