Here, I placed the pocket on top of the fabric I used for the back of the bag, cutting it the same size as the pocket, including seam allowances.
Turn and press as flat as possible.
This is a strip of coordinating fabric I used for a binding across the top of the bag, simply to cover the raw edges on both the pocket side and the back side. I wasn't sure it would work out, but it did!
Finger-press the seam you just stitched open.
Fold the binding strip down over the raw edge of the unit, folding under the raw edge of the binding strip evenly all around and pin.
I used a decorative stitch to top-stitch the binding down. I chose #27 from the list below. It gave good coverage for the binding edge and added some interest to the top of the pocket unit.
Then, I folded the strip so the fold edges match. I top-stitched the strip on both sides about 1/4" away from the edges, with a little longer straight stitch. I like to use a longer (about 3.0) stitch length when top-stitching because it looks more professional.
I stitched the (now) strap to the bag sides with a row of straight stitching, stitching across it twice for stability.
The finished bag!