Start with the contrast corner section and fold the fabric along the two short fold lines so the wrong sides are touching.
Now fold under the longest side of the Contrast Pocket.
Draw in the stitching line on the right side of the pocket. A quick and easy way of doing this is to fold over the pattern piece along the stitching line and use this as a guide as you place the pattern piece over the fabric.
Lay the contrast pocket over a corner of one of the bag pieces. Pin in place and sew along the stitching line on the pocket and through the bag.
You should have a pair of matching corners.
Now we can make up the rest of the bag.