Are the plants giving nice blooms? Are their leaves healthy-looking? If so, then the petunias are doing just fine.
I have some petunias this year in one of my raised "veggie" beds. They're not the tidiest plant in the world; they do tend to lie down and take it from there.
I've grown them before, and they were riotously happy with blooms for a good long while, but did it all while lying down on the ground.
If you expect petunias to stand up straight, like hollyhocks, sunflowers, or zinnias, then yes the petunias might look like they're in trouble. But whether in the ground or not, their flowers will end up trailing around...
Sunset Zone 17, USDA Zone 9