You can pass this. Begin a daily exercise regimen as soon as possible, preferably some sort of cardio, like running or biking. Don't ever skip breakfast. Eat healthy, cut down on toxins like caffeine or alcohol and drink plenty of water. This will not necessarily cleanse your system but it will significantly speed up your metabolism and burn body fat, which WILL help cleanse your system. You've got a good window of time.

If you still feel uncomfortable on the day of the test, just substitute. If you feel uncomfortable doing this (like me), then read the dilution sticky and follow it to da letter.