In my personal experience, you should definitely not fight it. If you rape and pillage a small village, you plead not guilty to try and dummy down the charges or enter a plea bargain. With pot possession there isn't much you can do, especially since you in no way excercised your rights. I had a friend who got caught and didn't remember granting permission to the park ranger to search him, so he thought about challenging it and saying it was an unlawful search. He decided not too and the judge let him off scot-free after an 8 minute speech.

Just admit it and be apologetic. Depending on your state law, a simple, low-quantity pot citation will not even create a criminal record, since it's a lower class minor misdemeanor in some cases.

I'd get a lawyer, though. NORML has strong roots in California.. you can contact them I suppose to see what they say. A lawyer can help you with the process of requesting no criminal record be made for you or expungement at a later date.