The way I reconcile C3-PO in my head is that Anakin assembled 3po more than he built him , I like the old lore that he was built on Affa or some such planet 125 years before the original Star Wars . I imagine he got in some kind of trouble and was disassembled and left in a junk heap on Tatooine and Anakin just found the parts and put him back together.
Well, that is literally what “happened” in Legends canon. I can’t remember the details, but there was a comic where Vader finds C-3PO’s head on Cloud City and then has a flashback to finding his disassembled parts (I think someone used him as target practice) in Mos Espa and rebuilding him.
The “you were meant to help this droid” is especially LOLable.