clear nail polish
Be careful with the nail polish. Some will turn yellow when you use wax or sealants. I say buy a small amount of clear coat from an auto body place or paint supplier. I think I had some clear coat in a touch up bottle at one time, but I can't find it now.
Cut a drinking straw at an angle and dip into the clear, then apply. Wooden match sticks are ok too, but need to be sharpened. Toothpicks work the same.
Here is my touch up routine. It takes about a week, but the results are very good. Recently, I use a magnifying glass if needed as my eyes are not as good as they were at 16.
Wrap some 1000 grit around a sharp edge and sand until metal is shiny, or if not all the way down, until the primer is showing but dont go through it.
Clean with alcohol.
Apply touch up with straw, toothpick, or match stick, and overlap the existing paint by only a hair's thickness or so.
Let dry for a day, then continue filling each day. It will take several coats to get it near even with the other surface. Add clear coat to fill the rest of the way up.
When level with other paint surface, use an aggressive polish until the areas are matched perfectly. I have used rubbing compound for speed, but it was an older car and had swirls so it didn't matter. I would use the most caution at this point as you don't want the area around the touch up area to look polished (or swirled) differently than the other parts of the car.
This sound like a lot of work, but the results have been good for me. Some people may not want to try this if they are not comfortable. I have seen some terrible touch ups. Actually my first really good touch up was to fix a bad dealer body shop touch up. My wife had a new car when we were dating in high school and someone chipped a piece of paint off with their door after she had it a few days. Against my advice, she and daddy took it to the "experts" at the dealer. Well, she came to my house crying because they put about 1/2" wide streak of touch up over a 1/8" chip and it looked terrible. Actually, the chip location on this car was right at a focus point on the door, so it stick out terribly. I fixed it with this method and it was good. Actually, I think this was the first time that they actually learned I was not a blowhard punk and could actually do something. After this I became the fixer upper for about everyone they knew, which was a lot of people in our hometown. This one fix lead to a lot of other work that I needed at the time. Funny how things work.