Are you putting it around the head or from nape-to-front? Just curious.
Martha Stewart once did a craft to turn ribbon into headbands.
She measured the ribbon, then took off 4-5"
Attach elastic to the ends of the cut ribbon, so that you have some stretch, which holds it in place.
My cousin did this cool thing on a headband that kept slipping: she smeared a thin bead of hot glue against the inside band, flattening it as she went, then let it cool/dry. It stayed in place because the cooled glue provides friction.
You'd have to test it though: it might melt the ribbon.