sounds like a conversation i've had many, many times (with myself) during my weight loss journey. i WANT to be more in control. but, some days i fail miserably. (like yesterday, for example.)
yes, you just accept the slip and move on. you have NOT ruined everything. the only way you fail is if you quit. and you're not gonna do that.
in the big picture....you will not go the rest of your life without an office potluck, or a doughnut, or a slice of pizza. eating these things does not mean you've failed. they are part of life. when there is a special occasion or a celebration...join in (in moderation). then, back on the wagon.
be kind to yourself. treat yourself the way you'd treat your best friend if she slipped up.
:-)