I'm confused by what you are confused about in the space to the left of the right foot ??
Let's see, I'm actually using Clayboard's scratchboard, and it makes a world of difference from the paper scratchboard and I highly recommend it. The paper ones tear incredibly easily and it takes away from the effect of the piece. Let's see- I wonder if you're talking about that white space?? Rockwell often places his paintings in front of a pure white background, I don't know how familiar you are with his work. . .
Can't wait to see your scratchboards, and good luck
Oh- if you 'botch' something, try using india ink to paint back over it then you can scratch that off again (scratchboards are india ink covered white chalk) which is why it will work. Sometimes the color of the blacks don't match up perfectly, but it's always worth a try.