You seem to be using the wrong basis for your calculation. My airline days ended some years back, but the basis was this (probably still largely valid):
Minimum ramp fuel at departure is:
Allowance for start and taxi (200 kg for B757/767)
Calculated sector burn;
Plus 5% of the above as en-route contingency (can be reduced to 3% if an en-route alternate is specified within a defined geographic zone);
Plus 30 minutes holding at destination;
Plus fuel from go-around at destination to nominated alternate, using realistic route and altitude profile;
Plus final "emergency reserve fuel" (around 400 kg for B757/767 size aircraft).