In retrospect, I had doubts, ultimately, about record (4)
I believe the answer is:
disc
'record' is the definition.
(eg a CD, compact disc)
'in retrospect i had doubts ultimately about' is the wordplay.
'in retrospect' says the letters should be written backwards.
'i had' becomes 'I'd' (I'd).
'ultimately' indicates one should take the final letters.
'about' becomes 'c' (abbreviation for 'circa').
The last letter of 'doubts' is 's'.
'id' back-to-front is 'di'.
'di'+'s'+'c'='DISC'
(Other definitions for disc that I've seen before include "Circular flat structure in the spine" , "Flat thin round object" , "Circle" , "In Olympic event" , "Part of flower" .)