Same thing happened to us, a couple of weeks after we bought it we got up to 1000 miles so started to increase the revs and for about a week or so it almost seemed underwhelming under accerlation. It certainly didn't feel as fast as the MK5 it replaced especially in the higher gears 4th and 5th. Can't really explain it in words as it would take an age to write it all down but both my wife and I kept saying it felt too smooth and not punchy enough. When we got up to 1500 miles I had really started to use the engine more and I would say taking it out for a real good thrashing at around 2000 miles has changed the engine. From 2000 miles onwards it has really improved both performance and consumption. Now up to 3000 miles and is really how I thought it should feel. All this is of course subjective and can be a lot do with the initial excitement of getting the new car then that dies down then you learn how to get the best from the engine, for sure though the MPG is much better now than when it was new and it is being driven harder.
Hopefully by the time you hit the 1000-1500 mile mark things will start improving.
