Since your anemone is very new to the system, the best thing to do at the moment is keep an eye on it, as far as that is possible with it in the shadow of a live rock. It needs to acclimate from the conditions it was in to your system. This will include water conditions as well as lighting.
I've had a BTA for a number of years now, probably added it to the tank before I should have, but it has not only survived, but split not too long ago. It was bubbly and fairly bleached when I purchased it, now the three I have are nicely coloured and all have rather long stringy tentacles. They host a Maroon Clownfish pair that is actively breeding. Maroons are natural species to host in BTAs by the way. Somehow I managed to luck in and my female is not as aggressive as others I've read about. She's fairly ok with me poking around in the tank whereas I've read some have drawn blood of their keepers whenever a hand presents itself. It really depends on each individual fish I reckon, but I really enjoy my Maroon pair and would likely keep them even if the female was a beast.
There have been a few harrowing incidents with the BTA over the years, one of them similar to your experience where it moved behind the rock work. This inexplicably happened well over a year after I placed it on a rock that I though was a fine spot. The first Maroon was already in the tank at the time, but took a few weeks to get in there. As mentioned the nem stayed put there for the longest time until making that weird move a long time later. I could barely see it but after over a month, could tell it was bleaching where it was. Rather than try to pry it lose I ended up turning the rock it was on, ending up in the inevitable major rescape, grrr. It worked though and it's stayed put since then, moving only slightly to allow room for the three clones that split off. I traded one of the clones a while back at a Kamloops frag swap.
To get back to your situation, if it's still in the shadows after a week or so and maybe a water change or two, you may want to try and move it to a better location. Aside from the necessity for good light, most BTAs will prefer a bit of a hollow spot in the rock where they can anchor their foot with some protection and stretch out from that.
Here are links to a couple of threads I started regarding my BTA. You might find them useful or of interest.
http://www.canreef.com/vbulletin/showthread.php?t=45902
http://www.canreef.com/vbulletin/showthread.php?t=54984