You essentially sealed your fate by answering the ranger's questions. I would recommend asking the prosecutor for a deferred resolution whereby you attend alcohol related education classes in exchange for the citation being dismissed or amended.
You state you got an infraction, is this correct, as infractions you just pay and doesnt leave a criminal record.
However, if your case is a misdemeanor or felony, they do leave a record.
You need to either look on your citation or call the court in order ot find out for sure, as there is a big difference based on whether it's an infraction or misdemeanor.
Please see my answers to previous similar questions:
Also, you emailed me directly regarding your questions. Please see my response.
As for fighting, all the prosecutor needs to prove is you were underage, and you were drinking. You admitted to drinking. That is enough to convict you. It would be best if you could work out a plea bargain.