Deleted
Posted: 11 Jun 2021, 07:15Deleted
In the main sector (bottom left corner) click with the right button of the mouse, opening a window, click on the sector settings, in the height and length set the desired size, then click on confirm.
I don't know if it's like that because I'm not in the game, but it's here. I think this can help you better:
https://github.com/SuperTux/supertux/wiki/Level-Editor