El capitan public beta installation stuck

I suggest you boot into Internet Recovery Mode, which should be available even if normal recovery mode isn't:

Boot to the Internet Recovery HD:

Restart the computer and immediatly hold down the Cmd+Alt+R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.

Partition and Format the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your newly installed hard drive. Click on the Partition tab in the DU main window.
3. If your internal drive is big enough for two OS X partitions (which is desirable so that you can have a stable 10.10.4 OS and a 10.11 side-by-side) then set the number of partitions from the drop down menu to 2.
4. Click on the Options button, set the partition scheme to GUID then click on the OK button.
5. Set the format type to Mac OS Extended (Journaled). Click on the Partition button and wait until the process has completed.
6. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Install button. This will install the version of OS X that came with your Mac Mini. Select one of the partitions.

Note: You will need an active Internet connection - Ethernet will be quicker than wireless because of the basic nature of the drivers in this state.

The exactly same think happened to me. I'm not freaking out because there are a few things I didn't backup. Yes. Stupid ME!!! Why did I do this. But the question is whether there is any way to recover the files with this Internet Reboot.

Is there? Or am I just f&(%??