Water parameters are ok, even the Calc at 350 is fine (on the low end).
Not much LR
in the tank, but nitrates are acceptable too.
Are you feeding it?
Has it moved around the tank?
Acclimation to aquarium life can be very difficult for the sebae anemone, They also tend to be Difficult to keep in captivity.
we should not try to keep anemones in our tanks. They are much better off left in the ocean where their lifespan is indeterminiate (30+ year - infinite - nobody knows).