The best thing to do is to not cut yourself to begin with. There are ointments you can use to help with scarring, but you need to fix the underlying problem here. Get help for your depression.
I you don't pick at a scab it usually will heal correctly without any scaring. Also scars usually disappear within 4 years, and if it dosent disappear or fade by that time and is still as bad as when you first got it, and it bothers you, you can go to a doctor to take care of that. Don't worry bout scars tho. I have them all over, and some life long scar on my face too. I don't mind tho.