I have had the same experience so I know how you feel. Yes, try to touch it up using one of the methods suggested above. Sand to smooth it down mask and spray paint would be best. Touch up paint would be quickest and easiest. Where it is located it doesn't need to be perfect. If you want a better job later take the bumper off and take it to a body shop and have it completely repainted. My guess is in a few weeks you won't even think about it anymore.
Pales in comparison, but last Thursday my fiancé and I went to Arlington Va for dinner after our getting off of work. As luck would have have it I found a free parallel parking spot close by. I may have parked a bit close; but when he first opened the door on the passenger side there was the sound of the the bottom of the door meeting the curb. He was torn up over it; since in the last two months of the new ride I have been parking in the far lots when we have gone out in the Prius. Till this day I still have not looked at that door. Stuff happens.... I am more concerned based on real driving about the frontend and the rear end given how low the Prius sits. One of the reasons I went with the Thule Raceway Platform vs using a hitch mount. I want to keep the Grey Ghost in a clean vs average or worse state when I want to trade him 8 to 10 years down the road...
I know how you feel. Just "knowing it's there" is maddening! I'm still waiting for my "first." Thought I had it a week ago when my door blew open and into the car next to me. Scratched that car a bit (yes, I told the owner) but the very small scape on the door edge buffed right out. The worry is just a sign of "true love!"