I bet you're good. Don't smoke until they give you the all clear.

If for some reason you don't pass, you could always act like you are completely offended and appalled at the fact that they think you tested positive for something, talk about you are a hard worker who needs your job, respects your employer, there must be some mistake, yadda yadda, and ask for a re-test. By then, you'd be clean for sure. I have actually heard of that method working. Practice your acting skills until the all clear, just in case.

Good luck. You are probably fine!