I've no personal experience of the Cdi, but that those numbers do sound low to me. Even my undergeared turbo-petrol will easily achieve those. But, hopefully some owner can offer a more meaningful insight.
While you're waiting, first obvious thing that occurs to me is have you reset the trip computer? The previous owners numbers may affecting your numbers otherwise. Second, it might be it just needs a good run on the motorway at higher revs (so, one gear lower than normal) and perhaps a nice tank of V-Power or 'ordinary' with a reputable injector cleaner in it. There are so many things that can get 'gummed-up' with modern diesels, it may be suffering from the previous owners use. If it shows no sign of improving after that, it may be you need to get it back to the retailer for a check over.