Help, Please! Neck Shaping!

So, I've read, and re-read the pattern.
I'm making the medium Size.

The way I understand it, is by the end of the arm and neck decreases, I should have done the total number of decreases as I did for the back piece (30)

The pattern reads that after 21 armhole decreases, I start my neck shaping -and unless I keep doing my math wrong, the neck shaping (for the medium size), at best occupies 7 RS rows (or 7 decreases (I'm counting the bindoffs as 1 "decrease row" - if that makes sense). The problem I'm having is this still leaves me short of a total of 30 decreases....21+7 does not = 30. What on earth am I doing wrong?! I've done my neck bindoffs, but don't want to go any further until I figure out if I'm doing it alright or not - I want to minimize my frogging, if you know what I mean.

Also, for the Neck Decreases: Are you guys doing the decrease right at the edge, or are you doing something like K1, then decrease (either K2Tog or SSK depending on side)?

THANKS SO MUCH FOR YOUR HELP!