You can do this one of two ways. First, go ahead a few days and add the ingredients in your food log. Once that's done, take the nutrition info it pulls up for your "day" and make a custom food for it.
Alternatively, you can go to another site (Google "recipe calculator") and build the recipe there, then make a custom food in FitDay with the resulting nutrition info.
And now that you don't have to be perfect, you can be good.