Amount pledged about minimum? On the contrary and quite wrong (8)
I believe the answer is:
mistaken
'quite wrong' is the definition.
'amount pledged about minimum? on the contrary and' is the wordplay.
'amount pledged' becomes 'stake' (a player's stake in poker).
'about' is a charade indicator (letters next to each other).
'minimum? on the contrary' becomes 'mi' (I can't explain this - if you can you should give a lot more credence to this answer).
'and' becomes 'n' (common abbreviation for 'and').
'stake' after 'mi' is 'mistake'.
'mistake'+'n'='MISTAKEN'
(Other definitions for mistaken that I've seen before include "Wrong in opinion, judgment etc." , "Wrongly understood" , "Wrong (in judgement)" , "Wrong, incorrect" , "'Wrong, misguided (8)'" .)