Some law enforcement agencies (including the FBI) secretly assume that even applicants they would want to hire will lie about having ever driven while under the influence of alcohol. Perversely, the more honestly a polygraph examinee answers a "control" question about driving under the influence, and as a result feels less anxiety when answering it, the more likely the examinee is to wrongly fail the polygraph. So yes, you may have been better off not disclosing your drinking and driving.

While you cannot unring this bell, unless you admitted to being a habitual drunk driver, your admission is unlikely to be disqualifying. If your polygrapher asks a "control" question about driving while under the influence, it may be rephrased as, "Other than the incident(s) you told me about, did you ever drive while under the influence of alcohol?"

When you answer this question "No," your denial will still be expected to be less than truthful, and if you don't react more strongly to this question than to a corresponding relevant question like, "Did you ever use an illegal drug?" you are likely to fail the polygraph.

For more on polygraph procedure and strategies for reducing the risk of a false positive outcome, see Chapters 3 & 4 of The Lie Behind the Lie Detector (1 mb PDF).