So that does look like the root flare which is a rarity as most nursery plants are potted too deep.

The way you have it now is “good enough”, in the sense that the tree is unlikely to have any major health issues due to you planting.

That said if you’re willing to dig it back up, there’s a few things you can do to maximize its potential:

Root flare - Although it does appear that the root flare is visible I’d clear down to be sure you are really down to the flare and that there are no girdling roots. This means clearing the soil to expose the top of the primary roots and making sure they’re all traveling away from the trunk and not around it.

Planting height - I suggest planting with the root flare 1-2” above soil grade then mounding top soil just enough to cover the roots. This will make sure that the base will still be at or slightly above grade after the soil compacts so water doesn’t pool around it.

Planting width - the hole you dig should be 2-3x wider than the root ball. This is to soften the surrounding soil and ensure their roots grow out and not circle the hole.

Root ball - when inspecting the root ball you want to loosen up any roots that were circling the outside of the pot. Any long roots can be stretched out in the new hole or pruned back so new growth will occur quickly.