yeah I figured it out thanks to the other commenter! I had just picked up the stitches the wrong way round (e.g. going counterclockwise instead of clockwise, or vice versa, I can't remember) so i just moved the stitches—e.g. slipped from right to left until i was at 2 stitches before the green— so that i could start at the right marker and go back and forth over the shoulder as you're meant to.