This sewing projects finished size is about 325/8 inches.
Proceed to read the instructions down below and watchMinki Kims video tutorial on YouTube as well.
Give it a good press, then cut it around leaving only a 14 inch seam allowance.

Image Credit: Minki Kim via YouTube
Trace the pattern on the lining fabric as well including the small square shape at the lower center.
Sew over the traced small square, then make notches inside the square, and trim it out.
Push the lining fabric through that small hole so that their wrong sides are now facing.

Give the lining fabric a good press to smoothen it out at the back.
Next, sew the gap close making sure to tuck the seams nicely.
Make a strap using similar fabric as the main fabric, fold, press, and sew.

Insert in a hook and attach to the D ring on the case.
*All these images are credited toMinki Kimvia YouTube.