Pin Scarf to ironing board, use a ruler or marked stick to measure width.
Get a pillowcase.
Soak pillowcase in water. Wring out excess water. Lay damp pillowcase over scarf. Set iron to "Wool" setting. Iron pillowcase over scarf.
Iron until pillowcase is dry over scarf. Let scarf continue to dry on ironing board. Unpin when dry.