Repairing scratched bumper tips

[sonicsoundzdj]

So I scratched my bumper the other day on my garage which has a pebble dashed wall so its a bit deeper then just a surface scratch. I would like to repair it myself if possible but need some advise before i go ahead with it so i don't make a mess of it. iv got a touch up brush with my colour already, could I use this to fill in the scratch and buff it after or will i need to sand down the whole area and primer,spray, lacour it? I also know that metallic paint is harder to blend in which might cause problems.

Any advice would be helpfull.Cheers!