If you eat in a surplus you will gain weight. Some will be water, some fat. Just eating in a limited time frame is not sufficient to loose/maintain weight. You need to keep yourself in a deficit for that. IF helps creating this deficit by limiting the time you eat, you basically skip one/several meals. But if you “eat back” those calories you skipped, or in some cases even more then you will not progress anything.
Clearly you ate more junk food than you thought. Could also be alcohol making you retain water, but just keep at it, the holidays are a tough time for losing weight so as long as you maintain your current weight you are doing fine and then you can get back on track in January.