Deep scratch! :(

[Clutch34]

So I just noticed a 5 inch scratch on the bottom of the back right panel behind the tire at the lower end of the car. I have NO idea how it got there or how long I've had it for!

It fails the finger nail test as my finger nail definitely gets caught in it. What can I do about it? Are there any preventative measures I should take before something bad comes of the scratch?

[Mike Phillips]

If the panel is metal, as in steel you need to clean and seal the scratch so it doesn't rust. So many cars are using composite materials for body components it's hard to be an expert on all cars and know what's what.

As for the scratch itself, get some touch-up paint and clean the scratch really well and then start filling it in. Since this is a lower panel this will be hard because you'll have to lay on the ground on your back and apply paint to a place that is going to be affected by gravity. So just put a little paint in at a time till you build it up. Assuming it's wide enough to put paint into?

Have a picture?