Well, if you were the commander then you should log P1. Whatever your friend wants to log is up to him. One of you was designated the commander on the ground before you got airborne and that person is the one who logs the PIC time.
If you decided that he would be the commander and log PIC and you would log dual as a student, then you're in an awkward situation and you need to do some real P1 time. If you decided that YOU would be designated the aircraft commander then you are fine - you have just incorrectly logged the time as dual when it should be PIC and he has incorreclty logged the time as PIC when he isn't entitled to log anything.
It all depends on which one of you was in command.