After withdrawing from the beta first, you can use Smart Switch on the PC to fully restore back to 6.1. However this will erase and wipe the entire phone. So back up your data before you do it.
As we discussed, you have been successfully deregistered from the Beta program.
Your current software will stay until the official software is released to the public, and you can rollback using SmartSwitch if you have backed up your data.
