Hello Mary,
Sorry to hear that - not what you wished for after the op.
I would be inclined to ignore what the urologist said about the oncology, and see what the oncologist says. They will probably be wondering, is this all in the prostate bed (possible due to positive margin), or are there mets in further lymph nodes?
Do you know what PSA was just before prostatectomy, i.e. how much it had changed since diagnosis? If it had gone up, then another PSMA PET scan might be useful. If not, it might not.
Given the known lymph node involvement, they might target the prostate bed and all pelvic lymph nodes. I don't know if this is done as a salvage radiotherapy, but there is a radial radiotherapy treatment which includes pelvic lymph nodes, so I don't see why not.
Wishing you all the best.