Problems while setting up buttons on the GUI

Hi,

I'm trying to set up buttons on my GUI in a way that the positioning will be ok whichever device i use (iphone, ipad), whichever resolution.

I thought it works fine because on the Game windows, it renders well with every resolutions (iphone wide, ipad wide...)

But when i compile on my device, it's totally different, the buttons are on the left, bigger...

If you have an idea about that problem...

Here is my script :

http://pastebin.com/ktj85287

Thanks in advance !