So sorry

Been there, done that.
Is this a weigh-in for a specific program, like WW? Or just your own personal weigh-in? I ask, because if it's not something absolutely necessary, you might want to forego the weigh-ins, particularly if a disappointing result might trigger you to go off plan. I say this because scales are such a poor indicator of progress and one moment in time just doesn't tell the whole story.
In my past, I found myself overeating both on good weigh ins and bad, if you can believe that! Unexpected good news was just as likely to trigger me to overeat as bad news. Almost a celebration, like WOW! I did so well; I'm going to eat to reward myself!
So I don't weigh myself anymore. I use other things as guidelines, like how my clothes fit, how I fell, etc - much like you did before you weighed. You KNEW you'd stayed on plan, and it WILL have eventually showed upon the scale. It just didn't at that moment in time.
If it's an official weigh-in, maybe you could ask them to only weigh you once a month or so. Or to weigh you and not tell you
As others have written - just shake it off and get back in the saddle. You can do this!