Honestly, I would leave it alone. See what it does. I don't baby mine at all. I plant .in in usually moderately high clay soil. Just throw rabbit manure on them once in awhile. Water in summer when it is super hot. I never pinch anything off, prune starting their see one year. Survival of the fittest on mine, as I want them to be around long after I am gone.
Sounds like it was a discount/clearence tree? Some of those are are dicey anyway, most as someone culled them for shape or age in their bags. Maybe the rootstock on yours (probably a dwarf) doesn't like wet feet. Could be transplant shock.
I grafted up dozens of new trees in 2016, two died, two the top stock died, the rest lived and are thriving in their buckets (still working on getting oak stumps out of the orchard area so I can plant them). Why did two die? Who knows... i did not do anything different than the others, and at that time they all overwintered in the same five gallon bucket. Some just don't make it.
Cedar