There is more than one way to do this. I wrote it out as close as I could to what the directions were calling for. There are as many ways to knit things as there are people knitting them.
You could also work the first 23 stitches, then continue with the same yarn and bind off the 14 stitches and work the whole right shoulder, bind it off and reattach the yarn to finish the left shoulder. No need for a 2nd ball, and certainly no need for a 3rd.
I think you need to read it again. Where do you see either 13 stitches, or 3 to bind off? There are 4 rows of binding off 2 on alternate rows, and then 4 rows of binding off 1. The back is already finished, you’re supposed to match the length of the front shoulders to the back. I don’t see anywhere to bind off 7 at the end…there should be 17 on each shoulder.