100% cotton linen? Cotton is one plant-based fiber and linen is another plant-based fiber. Each comes from a different plant -- cotton comes from the cotton plant and linen comes from the bast fiber of the flax plant.

So -- there is no "100% cotton linen" -- suspect that your fabric is likely cotton.

Nice job on the christening gown though - it's sure to become a family heirloom linen or not.