How long does it take for THC to clear out of your body?

I weigh 135 pounds and im 5'9 also pretty skinny so i assume i have a pretty fast metabolism knowing i eat like a horse. I rarely smoke the last time was maybe 30 days ago but i recently took one hit 5 days before my upcoming drug test. Its now 3 days untill my upcoming urine drug test. Yes ive done research and know i have to excercise and drink water. Do you guys think ill pass? Call me a goodie goodie but im freaking out knowing i only have 3 days left. Plz help me out.