1. You have admitted you were present for the crime and that you yelled you had a deadly weapon. Even if you have denied making this statement up until this point, there is a good chance if this case goes to trial, the prosecutor will dig up the admission some way or some how, increasing your chances of conviction.
2. What do you gain by going to trial? You have admitted guilt so there is little chance the jury will say forget about it, let this guy go. Worse case they will sentence you to the fullest for the crime, but most likely you will get minimum based on the crime, which in your case sounds like a felony.
3. Personally I would take the plea deal. You are going from a felony to a misdemeanor. In many states it is a whole lot easier to expunge or seal a misdemeanor than a felony down the road. A misdemeanor also, in most cases, will allow you to keep all your rights.
4. If you can afford an attorney, hire an attorney. Most public defenders (PD) are overworked and underpaid, and unless your case has some reason to stand out the unfortunate fact is that it will be one in a pile on someone's desk. Not to underestimate a PD, but there may be other options that an attorney with more time to review the case could find. If you have no adult criminal record you may also be able to plead guilty but have adjudication withheld. Essentially this means you admit guilt, the judge will sentence you of the crime, but if you complete your sentence it will not be viewed as having a criminal conviction and you will not lose your rights.
5. If you are honestly concerned about your criminal record, do you know how to get a hold of the girl? You may try to work a deal where your charges are dropped, or reduced further, if you are able to get the girl to turn herself in or point the police to where she currently is. People may call you a rat or snitch, whatever. This isn't about what someone thinks of you. You are facing real penalties and the possibility of doing jail time. In the end it is your future and you have only yourself to look out for.
Again, not a lawyer, but I have walked in your shoes to some extent.