My guess from what you said is that the end borders were ribbed and worked right on. So you began with some ribbing then went into whatever is the main body of the blanket. Then at the end you did more ribbing.
Now they are having you add some side borders (end borders are already there). Pick up 10 stitches along the ends of the ribbing section, then pick up 150 along the main body of the blanket, then on the other border pick up another 10 stitches along the ribbing that is there=170 sts altogether.