Any idea what breed and if it's male or female? I know nothing of ducks, just chickens.
If she doesn't look like a bowling pin when she stands up, she's a Khaki Campbell. Both breeds are very good layers.
Here's a picture from Metzer, with the hen on the left on drake on the right. You might have an immature drake, if it gets a dark head and a curly feather on its tail. It's probably a girl, however, and should lay like a Leghorn for you soon.