Well done Shaun. Don't beat yourself up over not showing you have any ability. You certainly had the ability to stand in front of Simon Cowell and the tv crew and sing your best. Its more than a lot of people could do.
I know, I for one, would not have the guts to stand up there and open up myself to criticism from anyone. You have come on "leaps and bounds" from your first audition. The best of luck with your future, you still have your whole life ahead of you. Don't worry about negative comments as you'll always have the begrudgers out there.
Again, well done mate, you proved you had the right stuff.