WARN: volume was not unmounted cleanly.

Hello everyone, hope you are all doing well in these odd times.

I'm having trouble setting up persistence on my usb:

I installed Kali linux onto my 64gb usb, I partitioned 20gb for kali linux and the rest for persistence named "persistence" as ext4.

The commands I inputted into the Terminal:

fdisk -l

mkdir -p /mnt/portable/

mount /dev/sdb2 /mnt/portable

Returns:
FUSE exfat 1.3.0
WARN: volume was not unmounted cleanly.

echo "/ union > /mnt/portable/persistence.conf

I went onto the desktop after this command, clicked the "places" tab, clicked 41GB VOLUME (no idea why it isn't called persistence) and double clicked persistence.conf

Back in the Terminal:

umount /dev/sdb2 && reboot

Rebooted Kali linux and none of the temporary folders are saved so clearly persistence failed.

Checked and read the Kali linux installation guide and typed in the terminal:

mkfs.ext3 -L persistence /dev/sdb2 (not sdb3).

This pops up:

/dev/sdb2 contains a exfat file system
Proceed anyway? (y,N)

I press y and continue and this pops up:

/dev/sdb2 is mounted; will not make a filesystem here!

What am I doing wrong? I've been following many youtube videos which are all similar except some create the persistence within Kali linux.

Any help would be appreciated thank you.