You know that you have the option to use @BIOS to flash right from Windows! I have a Gigabyte Mobo myself and I have used it for all of my BIOS updates, also on a few that I have done for friends. The @BIOS utility works very well, I have never had any problems with it, and you wont need to struggle with flash drives at all.
Download and run the utility, it will check for updates and download latest. If you need to install a beta version BIOS update you will nedd to manualy.
Since you already have the version you need, just plug in your pen drive and sow @BIOS the path.
Try it, you can't go wrong!