First cut your main fabric (on my bag it's the blue striped fabric). Cut 2 pieces that are 17 inches wide by 19 inches long and 2 strap pieces that are 31 inches by 4 inches.
Next cut fabric for the inside of your bag. Cut 2 pieces that are 17 inches wide by 19 inches long.
Next cut the fabric for your pocket. On my bag, it's the fabric with a floral print. Cut 1 piece that is 17 inches wide by 22 inches long.
Next, cut your fusible fleece. Cut 2 pieces that match your strap pieces.
Iron your fusible fleece to the back of your strap pieces.
Fold the straps in half lengthwise and sew up the long side leaving the two ends open. Turn the right side out (this can be a little tricky-be patient) and iron them flat so that the seam is in the center of the back.
Take your inner fabric and place with with right sides together and sew around two sides and the bottom.
Fold your pocket fabric in half so that it is 17 inches wide by 11 inches long. Place the outer fabrics together with right sides together. The pocket needs to go between these two fabrics. Sew down the side, across the bottom and back up the other side.
Now you are going to give each of your bag pieces box corners. To do this, hold your corners like this and sew across the tip about 1.5 inches down from the top corner.
Then snip it off.
Do this to all four corners. But you’ll need to be careful with the pocket and make sure it stays on one side of the bag and doesn’t get caught in the box corners in a weird way. I had to do a little seam popping to get it where I wanted.
turn your inner bag right side out and leave your outer bag inside out. Slide them together. Slip your straps down between the two layers and pin it in place. Make sure that it isn’t twisted inside and make sure that the side with the seam is facing the inner part of the bag.
Starting between two of the straps, sew all the way around the top leaving 3-4 inches between the straps to turn the bag right side out. Turn it right side out and press it flat. The corners should look like the photo: