The reason you join another ball of yarn is so you'll have a strand of working yarn at each shoulder.
So work across the first 17 stitches and drop that strand of yarn. With another ball, just start binding off the next 11 stitches, leaving a tail to weave in later, and work the final 17.
When you are working the right-side rows, decrease at the end of the first group of stitches, and decrease at the beginning of the other set of stitches. This will give you the decreases at the neck edge. Work the ws rows even. Do this twice more and you'll have 14 stitches on each shoulder section.
"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