For those of you that haven't tried to add ribbing to something, this is a good tutorial.

When I do mine, I sew the ends together to make a circle, then fold in half and put a pin in each fold, then put the pins together and add pins to the other folds. You will have 4 quarters, evenly distributed. Do the same for the item you are adding the ribbing to and then match the 4 ribbing pins to the item's 4 pins. Hope this helps some of you that are afraid to try ribbing.