Convicted of Simple Affray.. What are my options now?

About two years ago when I was twenty years old, I was out downtown (in public) with some friends. A fight ended up breaking out which I unfortunately became involved in. Two girls jumped on top of me and started hitting me all over my body. I felt like I had no choice but to defend myself. I started kicking and hitting the girls back to get them off of me. Finally, the fight died down and I got the girls off of me. One of the guys I was with was injured in the fight so the police and ambulance was called. The police took statements from everyone involved since there were no witnesses. The girls who jumped on me told the police that I started the fight. The police ended up charging all of us with simple affray and gave us court dates. I was never arrested or taken to jail or anything. When I went to court I was really confused. At first I was told I would be mediating with the other girls to come to a resolution. That never happened. I waived my right to an attorney, which at the time I thought meant I was electing one. When I got called to the stand I realized no one was there to represent me. The judge called me up and asked how I plead and I said I did not know. I told her I was defending myself and that I did hit the other girls but only to get them off of me. She asked again what I plead and I said that I guessed I was guilty since I did defend myself. I had to pay a fine of around $200-300. I do not believe I should have plead guilty to this charge, nor have it on my record. I feel like I was intimidated by the court system and pushed into making a decision I was not prepared for, nor did I know what I was doing. I would like to know if there is a way for me to either expunge the charge off my record OR reopen the case and plead not guilty. I do not want this charge to follow me for the rest of my life. Please advise.