how to fix the atc response when calling back the tail number and flight number ie. if my imput is correct say CESSNA 739LG I get a response CESSNA 739er LG 9er LIMA GOLF. should only be CESSNA 739LG ???

On the Main tab of Config, be sure you have:

Mfg: Cessna

Tail Number: 739LG

And be sure GA is ticked as the type.

You will then most often be referred to as Cessna Niner Lima Gulf, which is the correct short form.  You can also use the full call sign of Cessna seven three niner lima gulf, but that is the long form and ATC will most often use the short form.

Dave