Very few drug screens hold up in court!!!!!!! They are actually unconstitutional and the only way companies get away with doing them is by writing them into the private corporations policy and following that to the letter.
I used to be on the testing side, did you sign your paper before or after using the stall? Before- automatically cancel that test!!!
Did you initial the labels on the bottle or on the paper? - On the paper- cancel the test.
Dude get a lawyer and fight it- you can win. Most of the time companies do not know thier drug policies so they cannot follow them to the letter - any break in the COC and BAM the test is cancelled and they have to let you re-test...

51 ng, barely made it - fight it!!!!!fight it!!!!! You can win this one!!!