GC/MS confirmation of 19 ng/mL - Failed at-home test

A week ago I went to our family doctor and ran a full urinalysis and GC/MS to see where I was at with the amount of THC-COOH in my system. The test was taken Friday at lunch time, second void of the day, and my pH and specific gravity were all normal and the GC/MS confirmed I was testing at 19 ng/mL, much lower than the 50 ng/mL cutoff for a drug test I'll be taking on Tuesday.

This morning with my first void I did an at-home test (FirstCheck was the brand) and got the smallest line showing up that it could be negative. Wasn't a full line across, just one edge of the line. The box says that that's a test that would be negative for THC-COOH detection, but it's got me worried. I am fully aware that a lab that performed a GC/MS is going to be as accurate as possible (it was sent to a Quest lab, and I need to go to Quest for my actual test next week) in comparison to anything at home, but I'm still worried.

When I saw my doctor, I had been working out twice each day and drinking my normal amount of water I always drink (always drink a gallon of water each day just out of healthy habit. Last day I had smoked was Mar. 17, so from the 18th-24th I just didn't do anything but not smoke. The 25th through yesterday (Apr. 7th) I was working out twice a day, Insanity in the morning, 6-8 mile bike ride after work.

I'm just confused, as after two weeks off and working out hard for a week, I was tested at 19 ng/mL and now I barely get any sort of a line on an at-home test. Just causes concern. Anyone think I'll be good? Or should I resort to my buddy offering to help me sub? Was hopeful to just do this naturally, would feel a little better about myself if I had worked that hard and gotten it out of my system. Just worried. Anyone has anything to say, would appreciate it.

Also, I posted a thread last night that has much more detail, and is a bit of a long post, but if interested here is the link to that thread: DT next week! Help deciphering pre urinalysis + GC/MS

 

Oh, I am, very much so. I know this about myself, and I know it doesn't make something like this any easier for me. I've never had to complete a drug test before, and I've banked so much potential success on getting this position.... I just want to make sure what I've done to help myself out is actually helping.

Thankfully the doctor is a close family friend, have been good friends with his son since I was in second grade, and my current insurance takes very good care of me (haven't had to pay anything out of pocket for diabetes supplies in 4+ years). Was told it wouldn't be an issue for me so I was relieved to have that kind of help. I know I shouldn't worry in general as that's not good anyway for overall health and system, but just couldn't push the worry out of my mind. It's one of my traits I still need to work on.

I appreciate the response, though. Puts some ease in my mind about this. I haven't really seen many replies on here to some drug testing questions on the forums, so am thankful you took the time to respond.

 

Today is actually my last day at my current job. Supposed to start this new gig not next Monday, but the following. Have freelance I could fall back on for a little bit if need be, but really want this job for the career and life advancement I've been searching for in the last year.