Itsounds like this pattern:
If so, you start the shaping with 28 (30-32) sts. Then the directions are those you quoted for the shoulder:
Bind off 4 (6-8) sts at beg. of next row. Bind off 6 sts at beg. of each of next 4 rows worked from armhole edge.
Those directions should use up all the sts in each of the 3 sizes. For example, bind off 4sts, 6sts, 6sts, 6sts, 6sts=28sts for the smallest size. The same is true for the medium and large sizes.
If you have 8sts left over, you may have started with more sts before the shoulder shaping? Or you might have miscounted a bind off? Remember too, that you need to lift the given number of sts over and off the needle.
ETA: I just noticed that the directions before the shoulder shaping have you end the right shoulder on a wrong side (WS)row. That would mean that the bind off of 4(6-8)sts occurs on a right side (RS) row at the neck
edge. The following bind offs however at all on the armhole edge. I'm not sure that it makes a big difference but that is what the pattern directions are.