I just read another post, about someone who incubated wild mallards after the mom was killed. They onl have one stripe plus a half of another. this leads me to believe that the OP has indeed a mallard.
I actually think you have a hybrid mallard-rouen. The reason why I say that is that I can see very faint vestiges of a 2nd line under the first and a little line near the bill and the other spot where the ear is. A lot of the rouen hybrids at our lake looked like that when they were ducklings. Most of them grew very large like a rouen, but not quite the right body shape.