Get back about 100 too many (7)
I believe the answer is:
recover
'get back' is the definition.
(I've seen this before)
'about 100 too many' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'100' becomes 'c' (Roman numeral).
'too many' becomes 'over' (I've seen this in other clues).
're'+'c'+'over'='RECOVER'
(Other definitions for recover that I've seen before include "Obtain the return of" , "Get well again" , "Get better; retrieve" , "get fit again" , "Find" .)