Need advice please: I forgot I was expelled from school in 1999, answered "no" on the "has disciplinary action ever been taken against you in writing" question, and am now freaking out.

I was put on academic probation and later expelled from school the first time I went to college when I was young and stupid. I was reviewing my application just now, and realized I should have said "yes" on that question. It says "academic dismissal" on my transcript. It was in 1999, hence why it slipped my mind. I am freaking out. Should I contact the DI directors of all the programs I applied to and mention it? Or hope they don't notice? That seems sneaky to me. I don't mind them knowing it happened, it's been a long time.

I tried to change my answer now, but the option to save is no longer there, that I can see. It's after 5, so I can't call DICAS now, though I can call them tomorrow, but I figured I'd ask here.

Thank you for any advice. I feel SO BAD about this.

edit: I just wanted to add, I didn't make the connection in my mind that "disciplinary action" could mean academic dismissal; I thought it meant, like, if I had committed some crime or something. It was an honest mistake.