Don't smoke ANY MORE until AFTER the test, period. Drink a ton of water, and use a detox shampoo. Take a detox pill, if you can. drink at least 64 ounces (1 gallon) of water a day and pee whenever you need to.
The half life of THC is anywhere from 1 - 10 days. There's no way to tell for certain when it's out of your system, because there are too many variables, like weight, age, metabolism, etc.
Use a home drug test. If it comes positive in 5 days, increase to 1.5 gallons a day and check again 5 days later. If it's still positive, keep drinking lots of water and test in 5 day increments.
Also, wear nice clothes to your drug test, and if there's a plausible reason you would have your backpack (if there's no reason you would, just leave it at home. Overkill would make them suspicious), put a calculus or physics book in it, and maybe open it and read a chapter or two in the waiting room, if there's a line. They tend to be a little less wary of people like that. Just don't make it too obvious you're trying to look good.
Honestly, that's too much work for ME, so I steer clear of drugs. I'd advise you to do the same.
Don't do any more drugs for that time?
You shouldn't have smoked weed in the first place. It's stupid and unhealthy. Why? Ask yourself that.
Want to know how to pass a drug test, eh? Here's a genius idea. DONT DO DRUGS
Well as I've heard from numerous reputable sources, the best way to avoid failing a drug test is to refrain from the use of drugs.
Drink as much water as possible. Use the detox pill. The Detox shampoo! And if you can sneak it, have a clean friend pee in a bottle and stick it down your pants then pour that pee in the container unless they watch you, then just stick with the detoxing. Sucks.
Drink Plenty of water > keep pissing your brains out. Get a virus and take antibiotics. Take the antibiotics even without the virus. Won't hurt. But the antibiotics will show up on the test - and that's a good thing and once the tester understands from you that you've been ill, it might cloud his ambition to retest you for the weed. Good Luck