Answers please :)

kay
So I'm due next Tuesday and no signs at all but doctor says you can just go into labour all of a sudden but if I'm not dilated or baby isn't engaged how can my waters break as baby isn't pushing down or how can I start with contractions? I'm curious as I've been told membrane sweeps etc only work if your body is ready but how can my body be ready if there is no signs of dilation etc? Answers please