Fine plan, yet messed up (7)
I believe the answer is:
penalty
'fine' is the definition.
(I've seen this in another clue)
'plan yet messed up' is the wordplay.
'messed up' indicates an anagram.
'plan'+'yet'='planyet'
'planyet' is an anagram of 'PENALTY'.
(Other definitions for penalty that I've seen before include "Punishment; fine" , "Spot kick" , "kick by footballer" , "Disadvantage imposed" , "Fine - handicap" .)