You have 2 # 5 pieces right? And you cut one and one half inch off the tops of those two pieces.
Take one of the larger of the #5 pieces (the one with the interfacing) and place the zipper right side down on that. Right side of zip will be on right side of the fabric. Zip tab on the left side. Zipper tape will extend beyond fabric on the right side. Pin this zip in place. Now place the other large #5 (without interfacing) right side of fabric down, on top of the zipper tape. All three edges line up together. Zipper will be sandwiched in between the two #5 pieces. During this process, make sure that your zipper tab is just a bit over 1/4 inch from the left side. Sew using a zipper foot using a 1/4 inch seam allowance. After sewn, flip the fabric so that wrong sides end up together. You will end up with two pretty fabric sides outwards and the zip will be at the top and upright from the fabrics. When done, you will have the bottom of the zipper pocket completed. Do the same process with the two small pieces of the pocket. Let me know how you make out with this process. Like I said, I am not good at written directions. This completed piece will sit on top of #13 and no interfacing will show.