GC/MS question

Greetings drug testing aficionados!

This is my first post on this site, though I have depended on it for information since my first drug test last year, and I would like to thank you all for the invaluable information. :) I

I took my second drug test last Wednesday. I had to pee about an hour before the test, so I tested it at home and it looked good (reasonably solid line, light yellow). I then drank about 8 oz of water and about 8-12 oz of powerade, and dropped at the facility an hour later. It was not quite as pale, and a little more yellow. I was worried about what I dropped at the facility (I have learned that even people that don't use any substances have anxiety at a facility :P) so without drinking any more fluids or peeing any more I home tested my next pee about 3 hours after the test. It was even darker, but still passed with a faint line (I know, the faintness of the line isn't so important from what I've read). So I think I'm good, but I sure do still feel anxious. I feel a little better than I did all of Thursday and Friday though, because I haven't gotten that call from an MRO.

What is strange to me, however, is that I was asked to pay for the drug test (pre-internship). I know that a lab may send your pee away to a lab for GC/MS (at which point I would be in some deep poo), but I don't know for what reason they would except to confirm a positive test. I also know that it may take about a week if this is done, and that I would never know if it happened. Mostly what I am wondering is that if your pee is sent for GC/MS, is there an extra charge for it? (like, in normal circumstances where the organization pays, do they call the employer and ask if they want to pay for this to be done, or is it done at no extra charge?)

At any rate, I think I'm good, but it won't stop me from worrying about it. I have been trying to think about the best reaction to have if I do get that call. I'm thinking the best reaction may be shock, followed by concern for my health, followed by asking for information about when the toxins may have entered my system to find out what may have happened, and an offer to my supervisor to immediately retest. But, as I said, it's been 2 full business days already, so I'm thinking that if I don't get a call on Tuesday (Monday is Labor day) then I'm either good or my drop got shipped off to a lab.

Anything that you all can tell me concerning any of this would be greatly appreciated :)