I don't explicitly remember doing it, and so I'm obsessing.
But it would be worse to drive a half-an-hour to check, right?

You sound like me two weeks agoo, just before spring break.

Afterwards I thought "It's just something I do automatically, so I probably don't always pay attention to it. There's no telling if I forgot to lock it on not."

It happens sometimes, I really don't know why. Maybe I'm just worried my dad would freak and yell at me if we got broken into again (happened once about 10 years ago) because of me. At most I've walked 5 minutes back to my door to check once only though.