Is it okay to splurge on McD once in a while?

I have been eating healthy all this while but today I ate Double Cheese Burger with Medium Fries. Is it gonna ruin my diet? Usually I'd eat sandwich for lunch and consume up to 800-1100 cals a day, plus exercise 3 or 4 times a week. Lost 6 pounds last month. I'm gonna go climb stairs and jog later for an hour or more.