**warning** (nfin.pm:4) Model nfet device geometries will not be checked against the limits set by lmin, lmax, nfinmin and nfinmax. To enable this check, add a period(.) to the model name(i.e. enable model selector).
With warnings and errors like this one you simply have to do as you are told. A warning is not like an error, the simulation will still run but it may not have the correct results.