if you want to keep what you have, you can make the ribs disappear where needed.
the key is, to decrease so it becomes a line again, but it will be visible that is definite.
How many stitches do you have and how many do you want?
I would work the decreases in equal spots. (like once every quater, or even more often). Now you make one of the knit ribs "eat up" the neigboring purl ribs. on the left side, you knit 2 tog using the 2nd purl of the rib before. on the right side you ssk using the 2nd knit stitch of a rib and the first purl of the next rib.
that you do 4 times, then you ate up the 2 purl stitches and the 2 knit stitches to that side (of course you will not always use purls that disappear).
you can do that both left and right of the same rib or maybe on different ribs, but I would do equal amounts to the right and to the left to built symmetry.
the other option would be to finish the ribbing the way it is and then decrease on the knit section (first or second round). That will make the thing "rest" nicely flared on your shoulders.
PS: Some call them cowl or neckwarmer.