Hi and welcome to Knitting Help!
You're not going to be able to follow the written instructions for the moss rib in the same way that you have been doing. Instead you'll read the stitches that are on the needle and correctly pick up the pattern that way. It is important to maintain the pattern in the body of the sleeve.
So do the increase (I usually do the increase one stitch in from the ends and then incorporate that increase into the pattern on the next row). Then, using the sts from previous row as a guide, start several sts in from the end and count backwards, naming the sts in the pattern row. That'll tell you how to keep the pattern correct on the current row.