I'm sorry for your loss.
You're not going to like what I have to say. I'm sorry, I'm not trying to be rude, but, in my opinion this sort of thing happens all too often and it's perfectly avoidable.
It's very unlikely that it succumbed to an injury from rock, and next to impossible that a worm did it in.
I don't want to sound harsh ... but if I recall correctly, your tank is a 33g and it's only been set up for a month or two? I'm sorry but it was doomed from the get-go. That's one of the hardest, if not the outright hardest, anemones to keep. At the best of times, anemones are not easy to keep, definitely not beginner type creatures -- anyone who tells you different is either misinformed or misleading. If I'm mistaken, then please accept my apologies. But if I'm not ... The LFS who sold the anemone to you should have inquired as to your setup ... and you should maybe have done some more research first. There are plenty of resources out there. Read the Anemone FAQ .. it will get you started.
Don't beat yourself up too hard though. It's possible that it was doomed before you even purchased it. It depends on how well its cared for at the store, and then before they had it, at the distributors/importers ... and then before then how long it was in transit ... and how it was collected ... and so on. A lot of anemones at the point of retail are starved, and one thing that they do when starved is they start to digest their own tissue. You know this is happening when it's smaller than it used to be. This is very bad news. Even if they can start eating, a turnaround might be unlikely. And if they don't start eating ... it's game over .. maybe not immediately, but it's just a matter of time in those cases.
My advice for now is let your tank settle out a bit. A tank needs to be matured for at least six months before it's ready to house anemones. Anemones are pretty sensitive to changes in parameters and a tank that doesn't have that much time to it yet is simply undergoing too much flux before it settles into a sort of equilibrium.
After six months you could perhaps try a captive split BTA. A 33g should be a decent size for one of those.
Once again, I'm sorry for your misfortune ... good luck from now on.