Hi there ~
I understand your concerns. If your urine is positive for drugs and it has marijuana in it i.e. THC; the chances of you passing the preemployment drug test
is very less. I also believe that you need to wait it out, for another 2-3 months when you have not smoked to find out if your urine is negative and only then go in for the preemployment. The other way around it is to get a quantitative drug test for all drugs of abuse and show gradually lower levels in each of the weekly quantitative tests; while also obtaining a letter from your psychiatrist
attesting to the fact that you have either stopped or cut down on you usage of substances.
I hope this helps. Take care and have a lovely day!