The full size of the Fusion Drive is not available for repartitioning
Run the following command in Terminal: diskutil cs resizeStack ACA4133B-5F31-4D66-B502-4EABED4E2958 5E6D00FD-4BAD-424C-92CF-F8080CCC2C95 3.128t

The first UUID is your LV UUID, the second is the PV UUID that you want to grow (incase I mistyped one of them).

This will grow your disk back to fill up your 3TB disk. You may have to reduce that number to 3.1279t or something though. 3.128t should work. Unfortunately, you can't specify 100% like you can with many commands.