Anxious as part of guitar not quite complete (7)
I believe the answer is:
fretful
'anxious' is the definition.
(I've seen this before)
'part of guitar not quite complete' is the wordplay.
'part of guitar' becomes 'fret' (I've seen this before).
'not quite' means to remove the last letter.
'complete' becomes 'full' ('full' can be a synonym of 'complete').
'full' with its final letter removed is 'ful'.
'fret'+'ful'='FRETFUL'
'as' is the link.
(Other definitions for fretful that I've seen before include "Unsettled, irritated" , "on edge" , "Anxious" , "Distressed" , "Nervous and unable to relax" .)