I believe absolutely that there is no way OP can successfully claim he was acting in self defense and/or did not intend to hurt anyone when there was no intruder, no one to defend himself against, no actual threat to him or Reeva at all, only his GF using the toilet (at best) and he shot a powerful weapon at a closed door.
I don't see how anyone can be safe in SA from people in their own home if OP succeeds with his line of defense.