No, because with this limited data you cannot separately estimate the three components that make up a building's energy signature:
- the base load
- the base temperature
- the energy efficiency
Even if we assume the base load (i.e. the part of the energy used for other things than heating) is zero, there's no way you can estimate the base temperature (i.e. the outdoor temperature above which no heating is required).
If you assume that there were no casual gains during that period, then you can probably assume the base temperature to be 20 C, and only then can you reasonably claim that the energy efficiency of your building to be 11.4 * 1000 / (6 * 20) = 95 liters of gas per degree per day. Natural gas holds about 11 kWh per m3, so that's about 1.045 kWh / day / degree. That's very good (Swiss houses are between 4 and 10), whatever the size of your building, but it doesn't take into account your heating system's (in-)efficiency.