i need some advice

i took a urine test like 1 1/2 weeks ago for marijuana . well i sent it to the lab and it came back saying i still had 31ng of thc in my system...i have not smoked in over a month....how long should it take to get out of my system? i really need to pass this one... i got in trouble with cps for testin positive when i had my son so this is super important....:(

Theres no way of telling because each body is different. Periodic home testing would give you that answer.