Completely incorrect? Correct! (8)
I believe the answer is:
outright
'completely' is the definition.
(outright means completely or totally)
'incorrect? correct' is the wordplay.
'incorrect?' becomes 'out'.
'correct' becomes 'right' (right can mean correct).
'out'+'right'='OUTRIGHT'
(Other definitions for outright that I've seen before include "Total" , "Completely and openly - say a win" , "Unqualified - without delay" , "Completely and entirely, not gradually" , "Immediately; openly" .)