For the problem of sapwn you can fix that with skript :
command /setspawn:
permission: op
trigger:
set {Spawn} to location of block at location of player
On join:
teleport player to {Spawn}
But then, for the problem with the un-deletable world, idk XD... If you didnt try : log out and then in and try again and wait for it to say "Complete!" bc it have done the same thing for me and I log out and try again and it worked
I wish you good luck with your server
Warshwalow