Navigation DVD stuck

I tried to install a burned dvd dl Gen 5 map disc in our 2008 Prius GPS navigation DVD unit. The disc doesn't work (and I understand from reading forums on this site that it will not work)--but my real problem is that the disc will not eject, even though I press the button on the navigation DVD unit and slide it to the left. I read something about holding down the button for 5 seconds--do you do that when the car is on? When it is on acc? If the 5 second trick doesn't work, is there another way of removing the DVD, or do I have to take the whole unit out from under the driver's seat and open it up? Thanks!