Zigzag or overlock around all the edges of the fabric pieces to prevent fraying.
With right sides together pin the main fabric pieces to the lower section of the bag along its widths. Sew together using a straight stitch then press with the seams open. The bottom section should be in- between the main bag sections so when folded in half the darker section is now at the bottom.
From the right side of the bag, edge stitch along the seam line to reinforce and make a feature using decorative stitches or different colour threads.
Turn the bag round so the right sides are together / wrong sides showing. Fold in half.
Fold the two 10cm tabs/loops in two and pin to the inside of the bottom two corners of the bag with the loop on the inside and the raw edges together.
Starting from the top of the bag, with a 1.5 cm seam allowance, sew 3.5cm down and secure your stitches by locking off or reversing, leave a 2.5cm gap and sew the rest of the bag’s side all the way down over the loop, reverse several times over the loop to reinforce it.
Turn to the right side and press
Press the top of the side seams open for about 10/15 cm and turn the top edge over by 1cm, then over again by 2.5 cm, sew in place along the edge to make a channel for the drawstring.
To make the shoulder protection tabs: take the 4x 20cm webbing pieces and fold up 2.5cm on all short ends (wrong sides together,) press, pin and sew in place with two rows of straight stitch. 
Thread the drawstring cord around the top of the bag- Using a safety pin, thread one of the lengths of cord/ webbing through one of the channel openings, pass the second opening and all the way round to come out where you started. Do the same with the other cord length starting at the opposite opening.
Place two shoulder strips together with the turned hem inside, encasing/sandwiching the cord in the middle. Swap to a zipper foot, to sew along both edges to make a casing. Sew again but closer to the edge of the webbing. The shoulder tabs should run up and down the cord freely but snugly.
Knot after passing the cord through the loop at the bottom of the bag. Repeat on the other side.
The finished Drawstring Bag
