Answer me this...(spoiler alert)

Ok, admittedly, I may not have been paying enough attention, as it wasn't long before the movie began to wear on me, but, I was under the impression the piece had to be played flawlessly from start to finish in order for the key to be released. When he flubbed the ending during the concert, how was he able to release the key at the end by simply playing the last four notes correctly? Wouldn't he have had to have played the entire piece again to achieve this? Did I miss something?

Also, if I wanted someone to play an impossible piece of music, and needed him to do it flawlessly, and KNEW this guy had anxiety issues, I probably would have kept the screaming into the earpiece at a minimum. You know, for concentration's sake, if nothing else. Especially since he was already challenged with the added pressure of his wife getting a bullet to the head. Just saying...