[Why cant I make a superflat world?]

yeah I did and it still won't work which is wierd.

 

[Why cant I make a superflat world?]

For some reason it will not work at all. I looked at the tutorial and did everything it said and it refused to make a superflat world. All it does is make a new world that is not flat and its just like all the normal biomes. Can anyone help or have the same problem?