Spray petrol about inside centre (7)
I believe the answer is:
corsage
'spray' is the definition.
(I have seen 'Spray of flowers' mean 'corsage' so perhaps 'spray' could also mean 'corsage')
'petrol about inside centre' is the wordplay.
'petrol' becomes 'gas' ('gas' can be a synonym of 'petrol').
'about' says the letters should be written backwards.
'inside' is an insertion indicator.
'centre' becomes 'core' (core is a kind of centre**).
'gas' backwards is 'sag'.
'sag' inserted into 'core' is 'CORSAGE'.
(Other definitions for corsage that I've seen before include "Flowers pinned to dress" , "Part of dress" , "Spray of flowers" , "Flower worn on bodice" , "Nosegay, posy" .)