ok first of all, there is no such thing as MIXED register. its bullshit. you cant sing half-chest/half-head voice. its totally impossible. what you are feeling instead is when you go that certain pitch. you are at the lowest of your head voice. the feeling is somewhat weird. when i find the quote that i read from somewhere i post it up. right now its 3.20 am i damn sleepy.
i just heard your recording. am i right to say when you go that part, you push a lot and that most of the sensation is in front of your mouth? you are using too much air. keep the sensation at the back.
this will sound weird, but make a damn sharp sound quacking like a duck. the feeling should be at the back, a little high/upwards in the throat. when you sing high notes, you should aim in there. but do not aim all the way there as you will sound very sharp n shrilling. will hurt ppl ears hahaha. this will remove that airy sound, n u will still go up into that high pitch range.
and careful of your pitch on that song. good singers sing, and then they hear. great singers hear, and then they sing. so hear your pitch in your mind first, then sing.
anything just post it up i try to help
you might want to read up here
http://singinghow.com/how-to-sing-high-notes/