Fret not, the 5.3 l/100km is not the real world FC.it's what we call 'ideal conditions' FC.
many factors might contribute to this i.e traffic,weather,type of diesel used etc.
Anyhow,monitor the FC after a numerous fillups and it wil average out your FC.
From my experience,on my attempt to get the closest to the claimed FC,i only managed to get 6.1l/100km
And now that i dont really bother about the numbers anymore,my average running FC is at about 7.6l/100km
Considering my style of driving and the speed i go to,the figures are quite respectable IMHO.
Dont worry too much,check your FC again after several fillups then you might know the figure.
if you want to have a long term monitoring of your FC,i'd recommend Fuelly.
BTW,welcome to the forum and like everybody else,kindly introduce yourself in the Newbie section!