ok,
so its a 323 from 2008, that makes it an e90 or 91 (estate)
2008 BMW 323i (CA) E90 Sedan/Saloon automobile specifications and car tech data co2 economy fuel consumption
above is a link to the specs.
Personally, I think that even with the BMW efficient dynamics (stop/go) if it was available on this model, the car would struggle to achieve your claimed mpg.
Currently my best on a 4cyl 1.8 bmw using hypermiling techniques is 47 UK mpg, and that was on an extended Motorway run.
that is 39.21 US MPG.
My car is lighter than yours, with a smaller engine...so I dont see how your car can return these figures