View attachment 49659
It seems you have added the disk as a single disk vdev to the pool. You cannot revert out of this.
As far as I am aware the only option is to trash the pool and start again. You will need to copy all your data to somewhere safe first of course. You seem to have used slightly less than 8TB so it might fit on an 8TB drive (maybe) - but 10TB would be safer.
Actually - I think you could add another disk to the single vdev to make it a mirror which would get you some resiliency - but it won't fix the mess and you will always have 2 vdevs with one mirror and one Z1 which is doable - just not terribly recommended. This is assuming you have the capability of adding a new disk (Sata Ports etc). This might buy you time to get a bigger disk, copy the data to the bigger disk and then redo the pool. (during which time you data will likely be at risk on a single disk). All depends on what hardware you have available to use and its resources