remember the two added stitches on each side in MC.
with MC, CO 55 sts.
Row 1-10: work in stockinette
Row 11: cont. in St st while working the black keys on the charts
Row 28-38: cont. in St st w/CC; these are just the white keys
Row 39-40: w/ MC
w/ MC, CO 55 sts
Row 1 -40: work in stockinette
Sides (make 2):
w/ MC, CO 20 sts
Row 1 - 40: work in stockinette
w/MC, CO 55 sts
Row 1 - 20: work in stockinette
w/MC and size 9 ndls, CO 12 sts
i sorta guessed here. you can knit it however long you want your handles to be, switching it to white in the middle whenever you want, etc
next, you must measure your knitted Front and Back pieces. with these measurements, cut the plastic canvas to fit accordingly. also, measure the side pieces (this will determine how much lining to be used). make sure your lining is facing WRONG-side up. place your two plastic canvas pieces on the lining (remember to space them apart according to your side measurements) and begin folding the lining over the plastic canvas edges so the right-side shows, and secure them with paperclips. make sure you have enough fabric on the very right so you can overlap and paperclip.
sew all your knitted pieces together and slip it over your canvas/lining while also arranging the paperclips to hold the knitted piece to your interior. with your yarn and tapestry needle, start sewing the top edges together, then the bottom. attach the straps and you're done!