One step backward does not negate this journey!
It may help, on occasion, to say to give yourself "permission" to have a certain goodie - something really worthy. Eat it, enjoy it, and move on - guilt free. I know for me, if I deprive myself, that just won't work.
As for now, what's done is done. You now get a choice: keep yourself down and continue what you're doing, or lift yourself up and eat healthy for the very next meal you have coming up.
It's that easy, and that hard. But for long-term success, you have to learn to do it.
I know no other way around it....and trust me, I've been in similar shoes.
You can do it! Come on!! We all have bad days...and there's bound to be more throughout life. We all slip up. Just move forward. You can do it!