Nevada's statute regarding non-competition agreements, section 613.200 of the Nevada Revised Statutes, deals with this somewhat. The statute does not give employees the right to rescind a non-compete. It does require, among other things, that the agreement be signed in exchange for "consideration," which in plain English means, something of value. That could be money or a reciprocal promise of some kind. It is unclear from your question what you might have received in exchange for signing this agreement, since it was your last day. You should consult with a Nevada employment attorney to discuss your options.