The "squares" on your plan need to be shorter than they are wide. Your peg grid on the ground is in square squares: equal length and width. When you transfer your drawing to the ground, the figure on the ground will then be stretched out taller than your drawing, putting it into proper perspective for viewing.

The degree of "perspective" you add to your plan drawing (that is, how much shorter the grid divisions are than they are wide) is the same as the slope of the ground: the lower the slope, the more perspective (vertical squishing) you add to your plan drawing's grid.

Hope that's clear.