Well, how confident are you about the way the test went? Do you have an accent? How thick it is? Did you speak fast? If you answer is no, you might have a chance to get higher score.
Did you use idioms? Did you use topic specific words for section 2? Did you use less common words? If the answer is yes for each one, again you might get higher score.
But also, I think the further the markers are different from a native speaker, the more likely that the results could be different because head office most likely has native speakers as markers, whereas your local one has local markers. (My local marker seems to be obsessed with people saying "uhmm..". You say that and he will take off 2 bands, insane right? But I have seen model answers where people say "uhmm.." and still get 8, 8.5, 9). This is purely my speculation.