When you walk down the aisle just focus on smiling, most people are nervous being in weddings anyway. Once you get down the aisle try to just focus on the ceremony. That is what I did in my own wedding and people told me they couldn't believe how not nervous I appeared. I just focused on what I was doing and tried my best to ignore all the people. I know sometimes it is easier said than done.
So the girl has the wrong impression about you...prove her wrong. Like elek2ronik said, smile, be polite, ask her about what kind of music she likes. Have a good time and try not to be too hard on yourself!!