@Akabane been there done that when I was a teenager
"Sorry mom, time went by really fast, and I hurried back home as soon as I noticed and ...."
"But why you didn't call?"
<sudden realization> "ummm.... umm.... because I am an idiot?"
"You should have called as soon as you left the school, I was worried and you know the number and I though that..." <1 hour rant about every unrealistic scenario known by mankind where I die instantly>