The concentration was 3.3 nmol per gram of fresh weight.
Let's work backwards from your final result.
You took 1 mL of the cooled supernatant, and it had a concentration of 0,66 nmol/mL.
That 1 mL came from 4 mL of solution, so the solution must have contained
The 2 mL of original supernatant must have contained 2,6 nmol of compound before dilution.
That was a portion of the original 5 mL of extract, so the extract must have contained
The mass of your original sample was 2 g.
The concentration in your sample must have been