Really could use a better picture of the pot (does it have a hole in the bottom?), and the tree itself, but unless a trunk scratch reveals bright green underneath, your tree may be toast. Overwatering, unless really excessive, is not the most likely threat to Fukiens, but lack of humidity and bright light for lots of hours a day are. Without knowing more detail, it's hard to say though.

It does have a hole in the bottom for drainage, but we'll see how the next few weeks go!