To be honest, I dont think they will change the decision. It may well be other reasons than the one u have stated. Not being selected doesnt mean u are bad! Interview is like a game which u need a lot of luck. If the interviewers like u, no matter what crap u say, they may still think u are the suitable one. And, unfortunately, vice versa. Dont blame urself and dont try to pick out reason why u failed. It will only stress urself.
Try to prepare for the interview next year. In the mean time, do some more study, know urself well, prepare more. Next time u will make it!
U may think it's all bull****, but it's not. I have gone throught that years ago, and i failed at the last stage. It's even more traumatizing than ur situation! But believe me, dont loss ur confidence. Someday u will be flying again, just like me now. I am now with another major airlines.
PM me if u dont mind.