Help im freaking out over a drug test ?

I was a heavy smoker college I left about 9 months ago since then a casual bowl every week or other week. I smoked a month ago shared 2 small bowls then on saturday smoked a hitter and shared a tiny bowl with a friend. Had an interview I found out they were drug testing for so Thursday drank lots on Canberra juice coffee and about a gallon of water this morning had to take a drug test for the job. After the test that was supposed to take 10 min for results she said they needed to send it to the lab. I'm creaking out. Why would they need to send it to the lab and is there any chance I will be clean.