Uneven backlight brightness after keyboard replacement

Ive just changed the keyboard on my a1369 macbook air. Repair went well and now have a working keyboard with no issues apart from the backlight being uneven.

The left third of keyboard is fine, where the middle is brighter and the final third is a little dimmer.

I suppose Im going to have to take it apart again to get it right but I don't really want to be messing too much with the backlight.

I ripped my original removing the keyboard so I know how fragile it is. Well I wasn't really trying to be careful as I had bought a new keyboard that came with backlight...

What is the issue and what is needed to diffuse the backlight evenly as I can't think what I could of done wrong...