thears a bug

so when i join my own created world i created i cant do the cmds like gamemode cmds or any of it at all and stuff like that and also my game crashes and when i try to go back in it the game is privet i mean like it my game so it's realy not and the new up date u did to miniblocks to where u need to be like lvl 20 to make a new world it sys u need to deleate one and i did but it still says i still need to deleate one i did and it wont let me make a new one help but it still a good game keep up the good work