Messed Up Walls

I want to make a inside area lead to a outside area using a door but it messes up and if you look up you can see part of the sky and if you look down you can see bits of grass EVEN if the door isnt open!

is this a sector error? how can i fix it?

That's a bit vague. But you should check if the sector references are right.

Yeah sorry i don't really understand it myself, what do you mean by sector references?

sounds like the door has become an unclosed sector, delete the door and make it again

and while youre at it, a door leading straight to an outside area is bad news, give it a little doorway with a normal ceiling on the outside