Pre-Employment Drug Screen Sent to the lab? Help

Hi everyone. I havenâ??t smoked in 3 weeks. I was a daily user maybe once a day or less, 5â??4″ 160 lbs. Iâ??ve been drinking water, working out (not as much as I should have). I took two at home tests and passed both first void. I thought I was in the clear. I went in today to take a pre-employment drug screen. It was a morning appointment so i got up two hours early and drank two glasses of lemon water and a cup of coffee along with my daily multivitamin . I went two times before my screening. When i went in I gave my sample it was pretty clear but still had a faint color (kind of neon from my vitamin). I thought it looked ok. But the lady came back and said they had some questions about my sample and would have to send it to the lab (medtox i think) She then said we could not proceed in the rest of my physical and sent me home. Is it possible they found THC in my sample or maybe it was just to diluted? Please help, I am so worried. If they did find THC should I ask for a re-test? How long will it take to find out the results. I was offered this job and it is contingent on this drug test. I have a start date already too. Please help!