Setting up any RAID level under AHCI is not possible; here you have the first mistake.
You need to change SATA modes from AHCI to RAID in order to continue and setup operating system installation and RAID level.
I regret to inform you that you need to start from scratch because RAID structures does not work under AHCI even if you found the way to move it to RAID mode.
1. Enable RAID at BIOS level.
2. Reset disks to non-RAID
3. Recreate RAID array
4. Reinstall everything.
5. No chance to save any data.
