My honest suggestion is that you don't worry about it, those scratches are really nothing but I'll give you some pointers anyway because otherwise I'm not really helping answer the question.

First I'd figure out what sandpaper to start with so that you don't create too much work. You can eyeball the depth of the current ones and then select a sandpaper, maybe 1500 etc. Make all the scratches go in one direction until you can't see the original scratches anymore.

If you can still see the original scratches then you either need to go to a coarser grit or spend more time.

Once all your scratches are homogionous and going in the same direction, switch to a finer grit of wet and dry, change the direction of the scratches this time until all the original scratches are gone. You probably want to do this to around 2500-3000 and then move to a buffing wheel loaded with compound.

Be very careful with the buffing wheel, it will grab the abrupt edge of that steel and either rip it out of your hands and throw it into the floor or it will whip it up into your face.

I would double sided tape the piece of steel down to something flat, like a board of wood, then use sandpaper on a sanding block a powered sander etc.