The piston top is thickest in that area. Hopefully no damage to ring land. Pull the screw, grind off the sharp spots. Blending the screw might leave a part to fall off, possibly causing more damage. If you're not confident in your work, pop the rod cap off, and take the whole piston and rod into a machine shop. Maybe they can recommend welding, or maybe replacing single piston? Removal would be the best way to know if ring lands got damaged.