Crash and little ram On thin Snow

I created a superflat world using this code thing:

2;20,250x0,78:3;8;stronghold(count=7),biome_1,village(distance=0 size=0),decoration,dungeon,mineshaft

and the seed was

-7168682749803914668

I used creative. When I spawned, I flew up to the top of the world, when it ran out of memory. I reloaded minecraft and block one of the blocks. I crashed. When I loaded it back up, it looked like [pic attached], a line. There was a beginning point but it disapeared now. The block i broke was the beginning point. Up there it is laggy. I keep running out of memory up there.