Is this down to the metal? Damage to drivers door

[T1berious]

Hi there,

I'm hoping for some advice regarding a small amount of damage to the drivers side car door.



You kind of have to be looking for it to see it but my worry is if I don't address it, it could lead to rust or a problem further down the line.

Here it is zoomed in.



Door scraped a rock that was put on a grass verge (Nice!)

Can I get away with getting a touch up pen and polishing? its about 3mm x 4mm.

Any advice greatly appreciated.

T1b