You can't bind off at the end of the row. Bind off at the beginning of the armhole edge and then finish that row.
Then work back, decrease 1 at the beginning, work back, dec at the beginning again. Your armhole decreases are done.
Bind off as you normally would for those 4 stitches.
On the other side, you'll also do the bind-offs at the beginning of the row, but will do them with the opposite side of the knitting facing you.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry