( i've had my 2007 yaris sedan for a little over 2 months.. in silver )
So i noticed yesterday a dent/scratch in my driver door

(but not in the middle at the very end of the door towards the nose ) It's a dent about 2-3mm deep and several patches of paint were removed and some navy paint has been left behind. Entire dent/scrarch is about a square inch. Looks like a bike handle took a dive in my door.
My question is..
A. how quickly should i get this repaired before it rusts?
B. What will this cost me?
C. Or do i just need to buy a paint pen?
I'm a girl .. and don't know much about these things.. Wanted some helpful advice from people who know more about these things.. I know if i just go to the dealership they will just want to make an appointment and get it fixed right away.. But i might need to save a little money for that..
If a picture would help just let me know and i'll go take one.
Thanks in advance for your advice!