The main problem here is that you placed an understory plant in the full sun,
assuming you are talking about the same thing that I know as sourwood
(Oxydendrum arboreum). They like lots of shade, and very early fall color is a
good sign that the tree is not happy. I would find a tree that prefers full
sun as a replacement. I would reccommend asking the nursery staff about a
plants requirements before investing the time and money.

Toad