desperately seeking help

I have recently been put on probation (my first) and at my first screening I tested positive for THC, since then, I've had several negative testiings. I was baffled...I haven't smoked in almost 2yrs. I explained this to my probation officer (which I'm sure she's heard it all before) and she reported me to the judge. I have a hearing in a month...
Last night at work, I was discussing my dilemma with a co-worker..He said," Did you eat at @@@@ and ***** going away party??" I said yes. He informed me that some of the food there was made with mj and hemp oil. I'm relieved to know WHY I tested positive...however, now, I have a probation appt a few weeks prior to my hearing. Question #1. Do I report my findings to my p.o? Question#2.Do I wait and try to expain to the judge? Question #3. Do I just admit to smoking,say I have a problem, and beg for mercy?!?!?!I don't want to admit to something I didn't do, but I obviously don't want to go to jail (amongst other things).If I do admit to guilty, I violated anyway.. just think I'm screeewwwwed no matter what I do?!? I'm sure they've heard it all before.
Please...any and all advice with regards to my dilemma would be EXTREMELY appreciated!