Here is something to make you feel better about your big mistake:
on my application, I got one of my years for when I started colleg ewrong, so apparently, I've been going to college since I was five, and it took almost 20 years to graduate.
I also answered the question about having been disciplined because of academic performance with my answer for being disciplined for other non-academic activies. I ended up writing a letter to all the schools I applied to stating that the story of my arrest should be moved to the next question down...imagine how great i felt having to specifically point the adcoms directly to my less than glorious parts of my history.
There are plenty of other minor errors I've made on secondaries...but I wouldn't stress too much about the small stuff cause as that title of that book I didn't read because I was too stressed says...don't stress the small stuff.