I would be honest because it would suck to get into school and then get kicked out some time later, after they found out or worse, you go through 3 years of law school and can't get admitted to the bar, but I would meet with someone personally instead of sending something in the mail.
But I would be nervous if I were you, I can't see how you can prove it was a "honest" mistake vs. a deliberate one. That's a pretty critical piece of info to leave out of the application.