What are the directions at the beginning of the line you quoted? Usually on the back the two sides are balanced, so the directions at the beginning of the row may may help you understand how you should end the row.
It is an Easy Tank Top pattern by Lorna Miser and I’ve knitted the back until the armhole shaping part; that begins with:
Bind off 3 stitches at the beginning of the next 2 rows
Next Row: K2, ssk, work in pattern (which is 2 knits, followed by 2 purls) until last 3 stitches, K2 tog, K2.
Thinking it was an error, I went to several sites that list the pattern, but all I found was the same instructions, unfortunately
So to balance the k2, ssk at the beginning, you should work to the last 4sts, k2tog, k2.
“Bind off 3 stitches at the beginning of the next 2 rows
Next Row: [I]K2, ssk[/I], work in pattern (which is 2 knits, followed by 2 purls) until last [B]4[/B] stitches, K2 tog, K2.”