Sounds like you're in the same boat as everyone else in your round, right? It's simply a function of the timing of the deal (less than a year since you invested, apparently) and the deal structure (cash vs. stock).

Stock inherently requires the acquired company to share the risk of the deal.

If the stock goes down further, you should be able to claim the loss on your taxes when you sell, which should mean you would need more than a 52% total decline to go in the red on the deal.

Are you an accredited investor? If not, you may have some legal outs to demand your money back, but you'd need to chat with a lawyer. If you were to pursue that route, though, you'd likely ruin any credibility to make future investments in other companies.

Kinda stinks that there's the gap between tax law and SEC regs timing, though. Good luck with the investment!