help???

ok so I got caught 4th of july in canoe with two joints and to keep it brief landed on probation which I got put on last tues the 9th i had to see my po for the first time today. I wasnt expecting a drug screen but I got one needless to say I failed it. She is sending it to a lab to see what the levels where I told her I was going to fail it when she gave it to me. Anyway I have to go back on the 31 thats two wks from today and I need to be able to piss clean all bullshit aside anyone know what I can do to make sure im clean????????????