Accidentally made two volumes or partitions from the same new SSD

Hi,

I installed macOS Mojave on a new 1 TB SSD and must have somehow made two volumes or partitions with the same SSD. Under disk utility it shows this:

Time Machine will not work because "Two of the disks to back up have the same name". I can unmount the second one that shows 276.65 GB greyed out and everything is fine and Time Machine works. But on restart, it goes back to giving me an error.

Is it ok to "Erase" the second drive? Or should I click the minus symbol above Volume?