Dont know why this time it didnt work. heres what i did:

Made a blank world named Catacombs with the preset 1;0

tp'd to 0 1 0

filled 0 49 0 0 49 0 with sandstone 2

Tried to fill -48 49 -48 48 49 48 with sandstone 2 (it never worked)

Then i tried to quit and had to force quit because it had crashed