If you have clay soil and dig a deep hole and add amendments, you'll likely create a 'bathtub' effect. Poorly drained soil can rot Camellia roots. In clay soil, plant high and mulch the surface. Camellias are native to hilly Asian forests. In forests, there's typically a surface layer of rotted organic matter(humus).

I have lost plants to the bathtub effect and no longer amend the soil except for perennials and some roses.
I would lift the plant and only use native sol. Plant it high and mulch with pine straw.

I did both of these things at planting, though I did mix in peat and manure, as I have done for every single one of the other 18 to 20 camellias I have. These were both good suggestions. I went out and checked to see if the plants had settled to ground level. They do not appear to have. I scraped away the little bit of soil that was over the root ball. We'll see. They don't look worse for now.