For My Next Trick

I am so embarrassed. I signed the family up to volunteer in a booth for the SHADE Foundation at the finish line of the P.F. Chang's Marathon. We woke up today under the weather, so I called and said we were sick and couldn't come. The Volunteer Coordinator said "it is tomorrow." Oh goodness gracious, how did I do that? I originally put it on Saturday in my calendar, when I signed up, and, despite all the articles about the race, traffic congestion, road closures, etc., never noticed that it was on Sunday. How did I do that? I do know that the last race I walked in was on a Saturday. It worked out better to be home today for the beginning of our exterior house painting, but I will be continuing to wonder how I made such a silly mistake.