It sounds to me that your being "worried sick" is the biggest problem here. If you arrive at US Immigration and all sweaty and breathing heavily because you're nervous, that will probably cause them to ask all sorts of questions, which may well trip you up.

You are now much older than you were when you overstayed your welcome. Do you have now a job, a home, a relationship, etc. in Canada that would be a reason for you to return after your vacation in the US? I would think the assurance that you do not intend to stay to work would be important to them. What happened in your youth might be a "bad thing" but the present risks would seem to be more important.

Perhaps Firebug can chime in here?