Different people carry their fat in different places. Have you ever seen someone with a big belly and skinny legs, or a thin waist and a lot of junk in the trunk? Unfortunately, carrying fat in the boobs doesn't seem to be an option (damn!).
At any rate, I would have to say that your supposed weight gain is probably all in your head. I mean, eating a lot of fatty food isn't good, as you seem to know, but it takes longer than a couple of days to put on fat that stays. In order to increase your body fat, your metabolism generally has to slow down as a result of your body acclimating itself to all the new incoming calories, and that can take awhile (but not too long, so shape up!).
What's probably happened is that you feel self conscious about having eaten more than you're used to (hey, its the holidays!) and so you're paranoid about having gained weight and are seeing things where there's nothing. Happens to me too!