Wrong answer going in margins, plus grid's centre the day before (8)
I believe the answer is:
aggrieve
'wrong' is the definition.
(aggrieving is a kind of wronging)
'answer going in margins plus grid's centre the day before' is the wordplay.
'answer' becomes 'a' (abbreviation eg in Q and A).
'going in margins plus' becomes 'gg' (I am not sure about this - if you are sure you should believe this answer much more).
'centre' means to look at the middle letters.
'the day before' becomes 'eve' (eve is the night before something).
The middle letters of 'grid' are 'ri'.
'a'+'gg'+'ri'+'eve'='AGGRIEVE'
Can you help me to learn more?
(Other definitions for aggrieve that I've seen before include "Cause to feel sorrow" , "Make resentful" , "Ill-use" , "Cause annoyance to" , "Trouble" .)