At the end of the day; it's not helpful to you at this moment in time to be thinking like this. And again: this is only a small moment in the grand scheme of things. Look at what you've achieved: and it's amazing. Look at the BIG picture! Not the tiny little blip the other day: which is only natural. You really think no one else has had little lapses every once in a while?

What we do, is forgive ourselves for that moment, and move on. Start each day fresh and new. Start each day as you mean to go on.
It doesn't sound like your little mishap was anything emotional (which would indeed require you to do some soul searching), but it was more of going with the mood and swing of things at the BBQ! It's only natural for it to happen, I definitely know that sometimes allowing yourself to have a good time is better than being absolutely miserable and hence bringing everyone else down too.
So WELL DONE! On enjoying yourself. WELL DONE on pushing forward and acknowledging how it may affect you and realising that there are negative thought patterns coming through. You are doing very well; but never get into the habit of 'cheating' or 'compensating'. Just move on, it doesn't matter what the scales say: NO ONE IS JUDGING YOU.
You had some fun:
We're all entitled to some fun every once in a while aren't we?!?
So honestly. Calm down. We've all been there, this is exactly the sort of sitation when we enable what LL teaches us: and that is: to have a healthy relationship with food and our emotions towards it. Don't be scared of it. Don't always rely on 'weight numbers'. Learn to trust yourself.
:hug99:
And realistically. To put your mind at ease. It takes 3'500 EXCESS calories (on TOP of your maximum intake (around 2000)) to gain 1lbs. And that's a lot of calories. On Lite you're consuming around 800 per day. ... So unless you've consumed 4'700 the other day (on TOP of your 800!): you won't have gained any fat. Only glycgen back in the muscles. So if you do stay the same: one word of positivity: you
will have lost some fat, but it may not be showing due to water stores being filled back up and water retention.
....ok I should shut up now... I'm rambling like crazy.