Your whole chart is worked over 17 stitches. Row 1 is a wrong side row and it is K2, P13, K2. (are you calling the two edge stitches on each side of the chart shown ribbing? Or is there ribbing beyond what the chart shows? This is not ribbing on the sides of the chart, but reverse stockinette stitch.
Row 2 is right side and this is what you are to do there: P2, K1, YO, K1, YO, SK2p (this means to slip 1, k2tog and pass the slipped stitch over), k3, K3tog, YO, K1, YO, K1, P2. This uses up exactly 17 stitches and that is what you had, it also will cause you to end up with 17 stitches so you can work the next row (row 3) which will be the same as row 1.
Sometimes folks misunderstand a YO and think it uses a stitch, it doesn't, it comes between stitches only, forming a new stitch loop on the right hand needle. The chart seems a little funny, because it shows a K3tog and there are not two more stitches following that square to be used up on line 2 of the pattern, but they don't need to be there in row 2, but they are all there that you need from row 1 to execute row 2.