Serge all of the raw edges.
Center zipper tape along the 8 1/2" edge, right sides together, with the edge of the zipper tape next to the cut edge of fabric. Be sure zipper tab is facing down. Pin.
Attach a zipper foot.
Stitch close to the zipper using the center of the presser foot as your guide.
From the right side, press the fabric away from the zipper tape. Set stitch length to 3.5 and top stitch using the right side of the zipper foot as your guideline.
Line up the right side of the free zipper tape with the right side of the free 8 1/2" edge of the fabric. Pin
Stitch using a 2.5 stitch length. As your guideline run the left side of the zipper next to the right edge of the zipper teeth.
Finished attaching zipper on second side and ready to top stitch second side.
Press the fabric away from the zipper tape.
Open the zipper. From the right side of the fabric, top stitch using a 3.5 stitch length. Run the left side of the presser foot next to the fabric edge as your guideline.
As you approach the bottom of the zipper, make sure fabric lays flat and no extra fabric is caught in on the under side.
Second side finished top stitching.
UNZIP THE ZIPPER HALF WAY. With the bag still inside out, pin the side seams together. Sew side seams using a 2.5 stitch length and 5/8" guideline.
Side seams are finished.
To create more shape to the bag, open up the side seam and fold the bag in such a way that the the side seam lines up with the bottom fold of the bag.
The corner should look like a triangle. Pin.
Sew a stitch line one inch from the point of the triangle corner that is runs perpendicular to the side seam. Repeat on other side.
Turn bag right side out and press out corners to square the bottom of the bag.