My GSP does back flips... Only when I am not looking. J/k, sorry I had too.
The GSP will often take some time to adjust. Was it out and flowing at the LFS??
When I got mine it did take a day or two to fully open. And every once and a while if there is a change in my tank it will retract for a day or so. Give it some more time and it should come out.
That purple mat will cover the rock it came on, and then start spreading to the other rocks. GSP can spread quickly. Some folks like it to kinda take over the rocks around the original rock. I personally keep my little colony isolated from rocks, as I don't want it to take over my rocks. Just a heads up for you.