Figure 3

Figure 4
Figure 5
Step Four
Repeat step 3 on the remaining two sides. Note, when
you do this, you will end up with two flapping chunks
of border on each corner, as shown in figure 6.

Figure 6
Step Five
On each corner, one flap will seem to be on top of the
other. Fold this flap as shown in figure 7, folding
"C" to "A" on line BD. Pin in place. Press along BD
to mark line, and unpin. Pin top border to bottom
border, matching points within border, and sew along
line BD (figure 8). Trim seam allowance (this will
give you two triangles of border) and press.

Figure 7
Figure 8
Step Six
Repeat on remaining three corners.