Lay the piece of the main fabric on your work surface, right side up. Fold up one end and line it up with the other end so you for a 10" x 8 1/2" rectangle. Sew up both of the long sides, leaving the side opposite the fold open. Turn the bag right side out and carefully press all the seems.
Lay the lining fabric on the table, pocket-side up. Fold up one end and line it up with the other end as you did with the main fabric. Try to match up the pieces of hook and loop tape. Sew up both of the long sides, leaving the side opposite the fold open. Carefully press the seams.