wrong order given

I went to mcdonalds on my lunch break pressed for time i took just my order and rushed back to work as my lunch was almost finished came to work checked my order and it was the wrong burger that was given to me my order was suppose to be the spicy cajun meal and a big mac meal but they gave me a grand chicken burger instead of a spicy cajun which was so spicy i had to eat it because i was hungry i could not take it back as my lunch was finished and on the slip it shows a grand chicken burger but i specially told the cashier spicy cajun meal as i check the slip when i got to work as it was in the bag