RE: Finished Quantity in Finished Production Order cannot changed
I think your production order jumped a process, this is how it should've been executed:
1. Create Firm Planned PO. Change it to Released Prod Order
2. Book Raw Material Consumption & Output through Production Journal (Or Output Journal/Consumption Journal)
3. Change the status to Finished Production Order
In your case, the middle step got skipped. So please check your Ledger Entries on the Finished Production Order, there shouldn't be any Capacity Ledger Booked, nor should there be any consumption for the Raw Material. Analyze the ledgers one by one, if you do not understand something, please feel free to raise
Since your Inventory did not increase, nor was any item consumed (or any capacity booked), you can leave this Finished Production order as is