Taking a (fast) guess, it's just too weak to dig.
It seems pale, so it should probably get food regularly until it can establish photosynthetic algae enough to get any nutrients from your light-setup.
I had heard/read that they dig, but I could not get it to "root" in like that. I then heard, get a tube or cup (something with closed end) and dig it into a deep sand bed, put its base into it, but be careful it is not so deep that the anemone smothers there. Let it stay for a day or two before putting sand into the tube with it.
It worked excellent, but every time I have tried to let the Macrodactyla Doreensis >dig< by itself as online information claims, it have been unable and I believe it might be a common problem that people are always told they will have the energy to do it by themselves.
If the Nem is close to white in colour, it needs food until it gets stronger.