If it's something I accidentally missed, then you would have to complete it again. (Alternatively I can load your save file and alter it for you) But if its an issue with just the star not showing then it should fix itself! Im hoping its the second one aha
Viewing post in Bug Report Thread
To update on my side of things, I can now confirm that I started up the game fresh; went into Custom Night mode, selected Potluck, and clicked nothing else besides Play to start it up. Completed it on the first try of that session and still got no third star, so there definitely seems to be something tied to the star unlock trigger.