Use config setting 'world_edge' to determine size of world:

Defaults to '30000' if setting not found.

init.lua

@@ -2,7 +2,7 @@
 -- TODO: Check for terrain height
 
 -- Defines the edge of a world
-local edge = 30000
+local edge = tonumber(minetest.settings:get("world_edge")) or 30000
 -- Radius which should be checked for a good teleportation place
 local radius = 2
 --------------
@@ -140,4 +140,4 @@ minetest.register_entity("worldedge:lock", {
 	on_activate = function(staticdata, dtime_s)
 		--self.object:set_armor_groups({immortal = 1})
 	end
-})
+})