Just a clarification. BTAs split for two reasons.
The obvious reason is they grow too large to sustain themselves and must split (this is either genetic or environmental - you can decide). This happens at about 8 to 12+ inches diameter.
The other is poor health. In an attempt to sustain itself the anemone will split. The split is done in the hopes that at least one piece of the anemone will get away to a more a suitable environment.
Your anemone has most likely split because it is unhealthy. The most probable cause (IMO
) is lack of suitable overhangs or lack of suitable light. The best bet is to feed it however and whenever you can. What lighting are you using? What are your water parameters (pH, nitrate, nitrite, and ammonia, particularly)?
I'd also recommend you don't touch the anemone much. Leave it alone. They are quite capable of moving to locations that are satisfactory (if you have them) as long as they are attached to something.