Keep inventory didn't stick when creating realm, can't turn it on with console command

I tried to create a realm and turned Keep Inventory On, but it didn't stick after the realm was generated. I tried to turn it on by typing /gamerule KeepInventory true but I get an error message stating "cheats must be turned on to use this command". Cheats are turned on and it still doesn't work.  

I also tried making a new world with Keep Inventory on and using the "Replace" feature but that doesn't work either, I just keep getting a "failed to initialize" error message along with a message saying "out of hard drive space, maybe?", even though I have plenty of space on the Switch and in Minecraft itself