http://www.demigodthegame.com/purchase.asp
*We do not give refunds on beta software. If you purchased Demigod and are having problems with the beta, please contact support@stardock.com. Beta software is not finished and may have instability problems or bugs. We only give full refunds for problems with the released programs.
Says it quite clearly. Like Zubaz says, if you haven't actually downloaded any of the betas, you should be able to get it back, but if you have, then you're not going to.