When I back a bow with soft materials(rawhide, silk, linen, snake skins, etc.) I always do each limb separately and overlap at the handle. If you have enough material overlap it by 4" otherwise as much as possible. You don't have to go all the way to the tips either unless that how you want to do it. I usually leave the last 6" of each limb bare and bind that end of the backing with a wrap with thin, strong thread or sinew set in glue.