Don't panic. I got a RBTA the end of May and I went through nail-biting too at the beginning when it would shrink. The BTA likes to have it's foot hidden in rockwork, so moving in to a crevice would be normal. When it inflates, likely its tentacles will be in the light. It likely is getting acclimated to your lights, too. (BTW, what kind/wattage of lights do you have?)
My anemone has tripled in size since I got it and is doing well. It deflates regularly at night, and the bulbs regressed within a week and are now long with no bulb at the end (I have no clown for it to host at this time). It also defates when deficating (you will notice a brown gunk being dispelled from its mouth).
It also deflated for several days in a row which I determined was related to low oxygen levels. I have a crappy airstone-driven skimmer and it wasn't producing skimmate, so I disconnected it thinking it wasn't doing anything while I ordered a new airstone for it. Though it wasn't skimming, it was helping with oxygenation, and when I got the new airstone intalled, the anemone reinflated within hours, and has since followed its regular pattern. ( FYI; I determined oxygenation indirectly by looking at pH levels: CO2=Bicarb=higher pH, so if you keep a log of water parameters you can compare from previous and see if there is a change)