Maybe see it as an opportunity! Increase your filing skills!
I know mine could be much better!
Edit: I assume you mean the wedding bands and the short edges on the octagon corners leading to the wedding band. Not turning it from octagon to round.
I think it depends on how accurate you want to be. My guess from the picture is that it is not filed all the way round the barrel, and if you use a lathe, I would think it would go all the way round the barrel, wouldn't it?
I'm a sucker for doing things the hard way, and so I'd probably file it. Especially because I don't have a lathe either....
It's your gun, and I think frankly, you can please yourself and do it either way. Depends on how much you want to delve into doing things the old way.
Cheers,
Norm