You're probably working on the background layer, so create a new layer (Ctrl+Shift+N) and name it lines. Now select the Line tool (U) and connect the lower-left corner (point A) to the first point on the right edge counting from bottom up (point B).

figure 4

Now connect the second point of the bottom edge to the second point of the right edge. These are indicated by points C and D in figure 5. Keep doing these for the third, fourth, and other points. Your last two connections points should be indicated by points E and F in figure 6.

figure 5

figure 6

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