Punish and no mistake! (7)
I believe the answer is:
correct
'punish' is the definition.
(correcting is a kind of punishing)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for correct that I've seen before include "Accurate" , "Adjust, make right" , "See 6" , "Free from error" , "Rectify" .)