I Took Three Hits Of Marijuana From A Blunt On Sunday. I Have Been Clean For Five Months. Now I Have A Drug Urine Screen On Friday. Will It Show Positive?

I'm sorry to hear you had that slip up. Drink lots of water, it may clear your system. I've also heard that a vitamin product called Golden Seal will clear it but I don't know for sure on that either.
However it turns out, lessons learned I hope.
Auntimaime-

No it shouldnt drink a lot of water 1 hr before your test and don't pee. That should help you.don't smoke anymore. Stop while you can I smoked from 11yrs to 23 yrs and I have been sober 4 a yr now and my life has been great sense. Now a days to get a job you have to do random pissed tests.

Yes it should show positive. There are a bunch of ways to get clean quick, but by Friday I don't know. Marijuana stores in your fat. So drinking lots of water to pee it out will NOT work. You could try to sweet (Intense working out, in mabey some sweet clothing), but even still theres the time issue. No over the counter drugs will most likely work, as well as a clean up kit from a head shop. But you could get lucky anc not test positive.

Gtod may be right, but I've heard the Golden Seal tip too.  Never had to use it so don't know.  One could say this is one way to learn a harsh lesson.  Stay away from that stuff.  It never fails kiddo, when you use it, around comes the drug test. 

There is a product at GNC called Carbo cleanse. It works great for ua's.

You will be okay I am a recovering addict from a lot worse, I also am a unemployed lab tech.