? about at home tests and lab tests.

[yaboi128]

I just took a urine test at my new place of employment and they bottled up the urine so i guess their gonna ship it to the lab. On my way home i bought a lab quality at-home test. "first check" i think it was called. It came up negative for thc (yay). But i was reading the instructions and it said that it only works on fresh urine. My question is if my place of employment bottles it up to send it to the lab, wouldnt it not be fresh anymore? Is it possible that I get a different outcome than what my at-home test says (well i know its possible but is it likely?) Im asking because its been about 3 weeks since ive smoked but ive done everything i can to produce a negative result. Thanks in advance.