It's amazing how fast they grow. My little Khaki Campbells have outgrown two brooders. I don't really have anything bigger to put them in at the moment, so I try to take them out a bit during the day. When they hatched, they were only about 2x the size of the standard chicks that hatched at the same time (I had a situation where the first duck to hatch tried to tunnel out of one incubator to get into the incubator next door with a lone chick.)
My two babies hatched about 6-7 days after yours did.