[60041]

If you have only had the car a few weeks, the limited use you have given it will not be the cause of the warning light: provided the engine and fuel system is in good order, it will take many hundreds or even thousands of short journeys to clog up the dpf, your couple of hundred miles will have had no effect whatsoever on the dpf. I know of several diesel volvos that have done mainly short journeys for years without problems.
The obvious first check would be the oil level; these engines are very sensitive to being overfilled - if the oil level is high it will trigger the light. If it is, simply drain off half a pint or so and all will be ok.
The second thing could be the temperature sensor in the dpf; this is a well known issue on the XC90’s around about 2010 and 2011, when a batch of faulty sensors was used, it is possible your car may have been fitted with one if it is an early model. To diagnose that, your car needs to be hooked up to a Vida and have the codes read properly.