Step 6: Sewing the pouch--making the triangle bottom
While your pouch is still inside out, fold each of the four corners so the side seam is laying on the center bottom (see photos--this is hard to describe).
Pin in place and draw a line across the corner that is perpendicular to your seam allowance and, from edge to edge, is 2 to 2.5 inches long. The 2 inches isn't important but it is important all four corners be even.
Sew along that line (back stitch at each end to secure) and then trim excess fabric.