Sorry, go on mate (6)
I believe the answer is:
paltry
'sorry' is the definition.
(thesaurus)
'go on mate' is the wordplay.
'go' becomes 'try' (I've seen this before).
'on' says to put letters next to each other.
'mate' becomes 'pal' (I've seen this before).
'try' after 'pal' is 'PALTRY'.
(Other definitions for paltry that I've seen before include "Meagre; petty, trivial" , "Trivial, comtemptible" , "Trival, Inconsequential" , "Petty - base" , "Mean, petty" .)