Anxious as guitar part not quite complete (7)
I believe the answer is:
fretful
'anxious' is the definition.
(I've seen this before)
'guitar part not quite complete' is the wordplay.
'guitar part' becomes 'fret' (fret is a part of a guitar).
'not quite' means to remove the last letter.
'complete' becomes 'full' (associated in meaning).
'full' with its last letter taken away is 'ful'.
'fret'+'ful'='FRETFUL'
'as' is the link.
(Other definitions for fretful that I've seen before include "Unsettled, irritated" , "Querulous" , "Anxious" , "Nervous and unable to relax" , "Peevish" .)