Hi Jessica ... good to see you making a start.
It looks to me that you may have turned off too much wood on both sides of the center band, altho the nib end and the top end look about right
As for what sandpaper to use ... that is sort of up to your discretion and depends on how smooth the wood surface is at this stage. . As you get more and more experience with your lathe tools you will find that the surface, at this stage, becomes smoother and smoother.
I have a sanding sequence, starting with a slightly "rough" surface, that goes 180 grit, 240, 320 400, 600, 800, 1000, 1200, 1500, 2000
I only start at 180 if the surface needs some "adjustment" to remove slight bumps and hollows.
For a surface that is already quite smooth and only needs removal of "discolorations" I start at 400. . I never start at a higher grit.
I don't always go all the way up to 2000, but I always go as far as 1200 ... depends on what I am planning to do next and what finish I want.
Keep at it ... you'll get it !!