I'm having touble understanding exactly what happened? You went in to take a UA, were there for several hours and submitted several samples which were all rejected?

Yes, you should fight it if it comes back positive, but only if you are going to lose your job over it. They would undoubtedly test you again. It sounds like you smoke a lot of weed and sub for all your job randoms? Just be aware that if you challenge the results this may give your employer the right to have the drop observed, since something funny had to have happened in order to warrant the challenge of the initial results.

peace bro, don't let em get you down!