Keep repeating these rows but only do the increases at the ends of the rows indicated for your size in these directions until you have the number of sts indicated for your size:
Cont in pat as established, keeping cont of Chart, inc 1 st at each end of needle on next 0 (0-3-3-5) rows, then following alt rows 2 (3-4-11-15) times, taking inc sts into pat and ending with RS facing for next row. 57 (69-83-121- 149) sts.
You won't have sts left over because you'll keep incorporating these sts into the k2p2 pattern. This widens and shapes the back of the doggie sweater. One thing to note, you'll need to do an increase like a knit front and back (kfb) for the increases. When the pattern says inc in the first or the last stitch, that's exactly what they want you to do. You'll use up those first and last stitches on the increase.