Listen close. There is probably a 50% chance that you will piss positive, which is bad. However, as long as you can get your hands on the following, you should pass 100%.
Bottle of gatorade
Lots of water
Take a couple of fl oz. out of the gatorade, and fill it with a pack of certo. Drink this.
Take the B-12 vitamins (I don't know the dosage, probably 3-4 pills to be safe.)
Also, don't listen to people who tell you you're too young. Most of them are misinformed as marijuana has less negative side effects than tylenol or advil.
Drink as much water as you can.
The certo covers your kidneys so the THC can't come out in your piss, as it is filtered.
The b-12 will make your urine yellow so they don't think anything's up.
The water will seal the deal by getting out all of the THC that is going to come out through your urinary tract. Be drinking the water 2-3 hours before and up until the test, making sure your pee is yellow.