You're right where it's supposed to be, at 19 mpg.
https://www.fueleconomy.gov/feg/noframes/25165.shtml
It weighs 3500lbs, it's a small(ish) turbo-charged engine, it's a sports car...it's not going to get stellar fuel mileage whatever you do.
Yes, I know, how very unhelpful of me. Sorry, but ya gotta face the facts, IMO.