How long does marijuana last in my system?

I need to take a drug test for a summer internship within the week or so and I'm kind of worried that I won't be able to pass it. I took 3 hits of marijuana for the first time ever last Thursday, and I don't even know if I did it right cuz I didn't feel anything, didn't get high. I'm 5'2 and 150 pounds, 17 years old, and I have never done weed before. What is the likelihood that the THC will show up in a drug test?