The Parenting Version of Oversleeping a Final Exam

You know that nightmare college students have about sleeping through a final exam?  I figured out the parenting version of it today.
The girls, Oreo and I walked to their new school.  We walked around the back and talked about how I'd leave them on the playground in the morning and meet them in a specific spot after school.  I'll have Oreo, so I don't want to wander into the crowd.  I'll stand a little to the side.  Given the brunette twin's fear that we're going to leave her somewhere, I wanted to make sure she knew the system and was comfortable.
We were walking back when I saw one of their friends all dressed up for the first day of school with her backpack and a bunch of flowers for her new teacher.  My first thought was "Why is she going to school?  Do they really have school today?  How did I screw up the first day of school? AHHHHHHHHH!!!!!"  My second thought was "Okay, they cannot have school today because there isn't a crossing guard at the corner.  It's only Tuesday and they start school on Wednesday.  I don't see any other kids, so it cannot be the first day of school.  Breath.  Relax.  It's not the first day of school.  Breath.  Relax.  It's okay.  Breath.  Relax." 
Even though I knew it wasn't the first day of school, I felt a momentary panic.  The adrenaline rush stayed until we arrived home and I checked the calender.  I was certain, but I needed that black-n-white confirmation.