tuning PAG

Hi Everyone,
We have a database with
aggregate PGA target parameter                                    524288000
total PGA allocated                                                30632960
maximum PGA allocated                                             105198592
total PGA inuse                                                    22483968

total freeable PGA memory                                                 0
PGA memory freed back to OS                                               0
total PGA used for auto workareas                                         0
maximum PGA used for auto workareas                                71502848
total PGA used for manual workareas                                       0
maximum PGA used for manual workareas                                529408

Since our aggregate PGA target is >> maximum PGA allocated, we are wasting memory by setting the target too high. Is that correct?
I could not understand why no PGA memory is freeable , and no PGA memory is freed back to OS. Anything wrong with this picture?