I want to give you a big fat hug. Please don't hate yourself - no hate or guilt allowed! Everybody has rough times, bad days, up-and-down weeks, it's just life and you wouldn't be human if you didn't have the odd slip-up. One burger and fries never made anyone fat, after all! It's having several of them a day that would do the damage. You just had a sensible single one and it won't do you any harm in the long run at all.
Actually, eating something a little unexpected or naughty can actually kick your metabolism into gear a bit, believe it or not. Your body might have been craving the nutrients in a bit of beef and forced you to reach out for a burger. I'm willing to lay a big bet that you see good results this week, McD's or no McD's!
Just chalk it up to experience and above all don't beat yourself up. Nobody's perfect. If you can be good even just over half of the time, that means you still achieve your goals in the long term!