The bumper covers are made of plastic not steel.
I agree on layering paint base (color) coat layers over time to fill it instead of using Bondo since it is such a small area. You can also use toothpicks or these to apply the touchup paint precisely:
https://www.amazon.com/dp/B01N6D0207
The official Chevy touchup paint for my car looked fine when I applied it in the garage but it clearly does not match when viewed in the sun and I found others with the same complaint online.
This paint is a perfect match in the sun and the 2oz bottle I bought years ago is still perfectly preserved because it has an airtight seal. Other touch up paints I have previously bought from other sellers have not sealed well so they dry up over time and constantly release bad smelling fumes from the container. I would not recommend the 1/2 oz bottle from the seller I linked above because I bought 1/2 oz of primer in the same order as my 2 oz color bottle and the primer was already dried up the first time I tried to use it this year.