Worried-

Stop worrying, first.  It expends energy you might otherwise need 

Now, when you're polyed, the chart jockey may ask you questions about alcohol use/abuse, or he may not.  There are quite a few formats and subformats of polygraphs in use.  Some use control questions ("Have you ever driven drunk/been drunk/blacked out from drinking?"), which really aren't controls at all.  Some don't.  Some use controls where you are told to lie to the question.  And on and on.

Best advice: read The Lie Behind the Lie Detector, which is free and available on this site.  If you wish, start with Chapters 3 and 4.  They'll give you all you need to know about types of tests and their respective countermeasures.

That said, you shouldn't feel obligated to tell the polyboy anything other than what he asks.  If he asks about alcohol usage and you give him an answer from the Confession booth rather than a short, no-frills one, he's just going to inquire further.  You don't have to "come clean".  He's going to misrepresent himself to you, so you don't have to tell every peccadillo of your life (be honest, but just answer what he asks...)

Questions about alcohol use are likely "control" ones, anyhow, where they look to see if the question bothers you more than relevants.  It's bad science, but that's life.  However, if they ask,

"Have you been diagnosed as alcoholic before?"
"Have you had problems holding jobs due to alcohol usage?"
"Have you ever been convicted of DUI?"

You likely have a relevant question, especially the first two.  The third has reputedly been used both as control and relevant; when in doubt, treat a question as -relevant-, and I would this one.

Now, "Have you ever lied to your friends about alcohol usage?" is very likely control.  The PD or whoever is testing you doesn't generally care about how you respect or interact with your friends.  Two schools of thought on the answer to give: you can say "no" and set off the machine (given your statements), which isn't all bad: it produces a response, which can help you pass if it is higher than surrounding relevants.  Or you can answer "yes", as I would, and if they ask something about it, be ready with a generic, non-committal answer.

I would tell the truth and use CM's simultaneously, myself.  You can always say you were truthful (you were), and that you felt guilty about the question because you felt bad about lying to your friends (which is also true).  Thus, you've won with the truth and a little bit of physiological amplification.  Not bad

Good luck with your endeavors.  Live in the truth, but don't think a poly can discern it...