I did not add stitches at the underarm when I split off the sleeves.

After placing sleeve stitches on a US 4 needle, I picked up one stitches at the beginning, knit across the round and picked up one stitch at the end of round.
One the next row: K2tog, knit across round to two remaining stitches, SSK.
5 rounds of K1,P1.
Bind off in pattern.

I picked up the neck stitches with a US 3 needle and then switched to a US 4.
I worked 3 ounds of K1, P1.
Bound off in pattern.