Say you're trying to lie to someone about why you weren't in class or whatever. You blurt out the first excuse that comes to mind (maybe like "I caught typhoid fever", or something similarly hard to believe) but once you've said it, you immediately realize how terrible of a lie that was. So the (negative) emotion you'd get in that moment would be...?
The closest phrase I can find is "instant regret" but I swear to God there's an actual word for this feeling. It's not flustered, embarrassed, ashamed, humiliated, or any of the other synonyms for 'embarrassed' I can find.
An example that encapsulates that moment is the famous, We're all fine here scene from Star Wars
Also just realized it's probably an adjective I'm looking for and not a noun. D'oh!