Levelled (6)
'levelled' is the definition.
('even' can be a synonym of 'level')
This is all the clue.
(Other definitions for evened that I've seen before include "Made smooth or equalised" , "Made level" , "Levelled" , "Made smooth and regular" .)
(Other definitions for flattened that I've seen before include "Pressed, rolled out" , "Made level and even" , "Compressed" , "Squashed" .)