I wedged mine in between two larger rocks and it has continued to grow onto those. With a nice red one like that you could frag and sell some too! They are easy to frag, but don't cut in the main tank, they put out alot of goo.
You can take a pair of scissors and cut the outer edge off the entire way around. What you will basically do is make it smaller in diameter this way. That is what I have done when my toadstool leathers get too large.
Yours is doing that because it doesn't have anything to grow onto for added support. I'd do what Frantz suggested above if you don't mind moving it where there is more rock.
