Groove looks very good to me. Good job.
To polish the edges of the groove a little you may need to push sandpaper into the groove as you rotate the tube. I have an old piece of hickory ramrod that I use for this. I cut away 2/3rds of it for about 6" length, to create a "half-round" shape similar to a "half-round" file. This makes good backing for polishing wedding rings and flats, and turned on edge it should allow you to soften the edge of the cut groove a little. You might be able to just push it in there with your fingernail. I don't know.
When doing this polishing I use wet-dry paper. You can get decent paper at auto supply shops. I guess people use it for auto body and paint work. Maybe that's what you are using? I use a lot of 400 and 600, and occasionally higher grits.
If using a 1/2 round backing, it helps to dampen the back side of the paper BEFORE you wrap it around the backing, as well as keeping the cutting side damp while working. Dampening it first will help it wrap tightly around that 1/2 round shape. I just tear off a 1x2" piece and use that until it's dull, then get a new one. That works better for me than trying to fold it.
One important thing: If you can smell metal dust, then you are breathing metal dust. I always wear safety glasses and a dust mask when polishing. And I always and only polish wet. The paper is designed for that, and it helps contain the dust.
