You will need:
From fabric A (music notes) two 21" x 11 3/4" pieces
From fabric B (black duck canvas) one 21" x 9" piece
From fabric C (black lining) one 21" x 31 1/2" piece
From fabric D (black strap) two 15" x 3" pieces
From fabric E (notes strap) two 15" x 1 1/4" pieces
Fabric F is the pocket which you can make any size you like. You can also make outside pocket.
Not pictured interfacing same size as lining. Iron the interfacing to the lining.
I also used 1/4" seem allowance on everything.
First you sew together the two A peaces on each side of peace B.
Then you top stitch on both sides.
Next prep your pocket . I folded 1/4" on three sides.
Then i attach the zipper. Put right sides together whit unfinished edge and sew.
Then place the pocket on the lining I just eyeballed it and top stitched around.
and top stitched around.
Then unto the strap. Fold the black strap on half and sew on the long line. Then center the seem and iron the seam allowance open. Iron the note strap 1/4" on both long sides. Then top stitch the note strap on top of the black strap and your strap is ready.
You can follow this link to finish your bag. Good luck.
Here is the finish product.