Getting scratches out of floorboards

[purpleroad]

While sanding step I must have scratched the floorboards. Best to just sand it out?

Other photo shows floorboard loose. What are best nails to keep it down?

 

[Doggit]

Sand the scratched floorboard in the direction of the grain, but the other picture was too blured to asses. Do you have a cleat nail, or would a screw be acceptable, but do you know if there are any pipes under that floorboard that a nail or such may go through if yo have to mover the position of the nail.