Hey mate, i had a bit of bother when fitting mine, I had to get a mate to hold the spoiler firmly into the bootlid to bring the screw-holes close enough, then did up the 2 centre screws, then the top screw on each side and the bottom on each side.
As above, when you tighten it up, it will pull the spoiler closer in itself. Just make sure the brake light conenctor etc are out of the way. I just cut the plug off mine and spliced the wires together since it's highly unlikely it'll ever come off.