Importing camcorder footage into iMovie 09

Using a Sony HDR CX330 camcorder and I am desperately trying to get the best quality video from this as I am using it semi-professionally.

However, anything I film, once uploaded to Youtube, is 720, NOT 1080 despite the camcorder filming at 1080p. I realise there isn't a huge difference but would like to push my camcorder to its full capabilities.

On the camcorder, I am on dual recording, "Highest Quality", 50i. Once filming completed, I attach the camcorder to my Macbook and transfer via usb to iMovie 2009 in "full version".
I edit and export as an HD movie, but it always comes out on Youtube at 720.

An example of what I have filmed recently using above method:
https://www.youtube.com/watch?v=263lainFatM

Is there another method of import/export I should attempt to improve quality? There also seems to be a lot of flickering video (if you look between 2mins 13 and 2mins 18 - there appears to be lots of flickering lines?!)

Can anyone help me to make it 1080p and/or better my video quality in any other way!?

Many thanks