I would bind off the first 13, attach a new ball of yarn, bind off the center 29 and finish the row. Now you'll have a strand of yarn for each side so you can work the decreases at the same time on each shoulder.
Then, as you get to where the beginning edge of the neck is, you bind off the 5 stitches.
So on the next row, you'll bind off the first 13 on that side and work to the end. Bind off the first 5 on the other side and work to the end. Turn the work, bind off another 13, work to end. Then bind off 5 at the opposite neck edge.
You have to bind off at the beginning of the rows, so bind off at either the shoulder edge or the neck edge when you're at the beginning of the rows.
To measure the armhole depth, hold a straight edge across from the first decrease and then measure straight up to the neck--not along the curve.