Downloaded Windows on the wrong USB, drive is now formatted, how to revert back to before?

I bought a key for Windows 10 and I had two drives plugged into my computer: a flash drive that was meant to get the Windows installation, and my external hard drive where I keep family photos and files. It was 3 am in the morning so my judgment and awareness wasn't the best, so when Windows asked me to pick a drive, I chose my external hard drive. When I realized what I had done, it was already too late. My drive has a different capacity now (http://prntscr.com/i7sfrr), went from 500gb to 30gb, not to mention I lost my files.

Submitted January 30, 2018 at 11:55PM by gestioco http://ift.tt/2GsYTTY