Now I was creating a world and realized I left it on "Default" setting when I wanted it on Super Flat. So I quickly left the map then created a new one on "Super Flat" relatively fast, the I see I spawned on the exact same "Default" map, So I flew (I was in Creative) around a bit, and realized that I had managed to join the 2 worlds together somehow, I think I did it by going in and out of worlds so quickly, I tried it again but it didn't work. So I have no idea how it happened.

Additional Notes

If you want to download the map just comment and I will upload the map.