It might do, as couscous is carbs, rather than protein of chicken. Best advice, just drink water and get right back on track. You'll probably be fine if it's just the once and you didn't have loads.
Don't worry about it, as you'll make yourself feel crap, and might think you have come out when you are ok.
Tiny mistake, thats all it is. If you need to substitute though (I don't suggest you do) choose a protein, different meat, and a smaller quantity.
Sorry I can't be more use.