Power calculation in regression for curviliear effect


I performed a regresson analysis to test a curvilinear effect.
I've followed Aiken & West procedures
Center X,
Squared centered X

Enter X 1st step
Enter X2 2nd step

However, in the interpretation of the results I would like to test the power of this regression, considering the sample size.

Can you help me with this? I usally use Gpower 3 for power/effect sizes/sample size calculations, but I don's know if it is the adequate procedure in this time.