There are no magic pills or potions, so don't waste your money on 'em.

What is your size, age, metabolism and smoking history?

You can exercise now, but stop 3 days prior to the test and start taking a creatine supplement. Read the dilution sticky.

Get some home thc tests and test yourself. They suggest first morning urine, but in your case, I'm afraid that would be dirty with such few days clean. Try with some dilution about the time your test will be and see where you stand.