Step 4: Pin and Sew the Shell and Lining Pieces
The right side of fabric is the pretty side, the side you will see. The wrong side is the ugly side, which will be trapped with the seam allowances between the shell and lining and won't be seen. This part is tricky, so read carefully. For the shell, you will pin right sides together, and the shell will get turned inside-out. However, for the lining, you will pin right sides together, but it will not get turned inside-out, because the interior of the bag is the pretty side. This means for the shell, the right side is the OUTSIDE of the bag, but for the lining, the right side is the INSIDE of the bag. The pictures and notes will help you a lot on this step.
Pin the front, rectangle, and back lining pieces right sides together, as shown. Mark with ruler and trim excess from rectangle piece. Sew with a 1/2" seam allowance.
Repeat with shell pieces, noting that the diagonal should run the opposite way.