First off, congrats on the 10lbs lost! You are doing great and must have some good skills under your belt from the last 2 months.
Hope you enjoyed those vegetables (wouldn't everything taste better if mozzarella had 0 calories?!)! I sometimes miss details like that too, head in the clouds or something.
Maybe go for a walk and mentally know that you eliminated a few of the calories.
Like CanadianCutie said, one slip up isn't a big deal. Getting back on plan and back to your regular plan is a must at this point though! You can do it!