The contour interval has nothing to do with the scale of the cross-section. If you place a ruler with inches against the graph, you can see how many feet are represented by one inch. Then convert it into inches and that will be your vertical scale. As for the valley shape, it was just a slip of my hand when I was correcting your profile. It should be symmetrical, but that wasn't why you lost two marks. It was because you go high enough on the peaks and you didn't start low enough or end high enough on the profile."