Should I leave the drug test to chance?

Hello all, for the past two years I've been interested in this IT apprenticeship and after 3 interviews I got an offer for the job. To my disappointment the offer is contingent on passing a drug test and background check. Background check is no problem, but for the past few weeks I've smoked every other day. Originally the start date was set for Feb 5th but I told them I might have to wait till the 20th. I didn't say why. My question is should 1 try and decline the offer and go back to the waitlist if possible, or should 1 try my best to detox for the test. I'm in VA were weed is kinda legal so l'm also wondering ifI should just tell them my concern instead of taking the test and leaving it to chance