When they say that your polygraph results were "unsuccessful," which is more than likely to happen, do not confess to a single thing that they could use against you to deny you your clearance. (see 13 adjudicative guidelines) 

"Failing" "Passing" the polygraph is not about whether they notice a rise in physiological reactions, those are simply cover up terms for the polygraph's true intention. The true intention is to extract derogatory information from you that they could not have known based upon background investigation alone.