Yes, if I were you, I would watch portion sizes.
You can also request low-cal or low-fat/low-carb/low-sugar meals. (most caterers now-a-days must offer a wide variety of these meals because of so many folks with food sensitivities and requirements.)
Since you have been carefully following your own caloric intake for the past month on fitday, you probably have a fair idea of which foods are loaded with calories and which are not. So you might be able to make a fuzzy calculation for each day without a computer.
If all else fails and you gain back a bit next week....you KNOW you have been successful already...it won't take long to surpass the 5 pound loss!!!