A RAID needs to be setup before the installation of the OS.
This is true.
Therefore, you will need to do a complete start over and reformat both then turn on RAID1.
You'll need to eneable RAID in the bios. Upon reboot, go into the raid config and set up your drives in a RAID 1 volume. Then when installing the OS you will be given the option to select the raid volume as the installation disk. At that point, you'll be given an option to partition and format the raid volume.