The best way to calm nerves is to NOT practice the music the last two hours before the performance. If you do practice in this time, you will probably freak out and create some errors in the playing that were not there originally. Do not dwell on any one part of the music. Listening to recordings before a concert is also a bad idea. They wil make you self conscious and change your ideas about the music. We wouldn't want things like that happenning before a performance now do we?
To calm down, watch television or something to get your mind off music. You need to have a fresh look on the concert stage. If the audience senses you have worked hard on something and are still working details out, you know you have failed.