I think it's probably because you only have a stone left to go that you've started to slip hun.
Just think you could be there by this time next month, all you have to do is focus.
Have you thought about moving up a plan? Maybe you could spread your extra calories out during the day so you won't be tempted to binge? Or how about when you feel the urge to binge take yourself off and do something else... go for a walk perhaps, or maybe a bubble bath?