You can probably salvage it. Same thing happened to me - I bought what I thought was a marimo ball online ( can't remember the seller ) about a year after having it, same thing happened and it was not a ball at all! I felt ripped off!
I trimmed the edges off and its in my tank to this day ( although flat like yours ) the shrimp love it so I guess its okay,.
Oddly enough, the ones I have had from Petsmart for 5-6 years are still shaped like a ball ( orange size )