Agreed. I try to not obsess over any one moment, especially if that moment is a rare occasion. It sounds like today was out of the norm for you, so I would be inclined to ease up and move on. Trust me, 1700 calories in a day, combined with the excercise you've already done, is perfectly reasonable and not something to beat yourself up over.
The key, to me, is balance. Forcing yourself to endure over 2 hours of cardio to "undo" 300 extra calories seems slightly extreme to me. Remember that it's rarely one slip that leads to gaining weight - it's the not getting back on track as soon as possible afterwards. Cut yourself some slack and aim to have a better day tomorrow.
