Good advice – remember also that the area shown on the Strata Plan may (and usually does) include the area of any carspace and/or storeroom that “forms part of the Lot”, although the 2m² that you seem to have gained is insufficient for that to be the case.
The definition that “Scotty’s” provided is the one that’s commonly applied to a measurement of “floor area”, whereas your Developer is quoting “metres internally”, and as they’re sometimes as tricky as their measurement definitions, I’d take-up the suggestion of spending a few extra $ on having your Unit expertly measured before you make your final committment.