I have experimented with marijuana in the past (under 15 times within a span of 5 years).  I *did not* record this in my security forms; this is because my family was present for every subtlety of the forms and it would have been too difficult for me.

As I see it, I have 4 options:  

(1) Call the NSA right now and ask them to make a note on my security forms.  I fear they would make me fill them out again entirely.  I know for a fact that I am competing with 2 other people and the first one to complete the background check/polygraph to get the clearance gets the job.  So redoing the forms at this point would be the end of any chance I have.

(2) Tell the polygraph examiner right away.

(3) Tell the polygraph examiner after we go over the questions.

(4) Lie on the exam and then make an admission during the interrogation.  This may sound crazy, but if I make an admission perhaps the examiner will be more inclined to believe I am telling the truth and have done no serious drugs?  I have read that if no read admissions are made, the examiner can become suspicious.

Right now I think going with option (2) gives me the best chance, of course I am not sure otherwise I wouldn't be making this post  :-X