I noticed that the sump plug dosnt sit flat, its on the corner of the sump which will make it impossible to get all the oil out . I was worried that when the oil is changed there will still be dirty oil in there mixing with the new stuff
You'll never get it all anyway. It'll sit in all sorts of places. Oil cooler will also hold a bit. Change it regularly and it'll be fine. Could always flush the engine, but I'm not so sure it's a good idea.