Error: Kernel panic-not syncing: VFS: unable to mount root fs on unknown-block(179,6)

[jplank]

When I try to start up my retropie I get an error that prevents me from continuing the boot process. The error says:

Kernel panic-not syncing: VFS: unable to mount root fs on unknown-block(179,6)

Originally, the error said:

Kernel panic-not syncing: VFS: unable to mount root fs on unknown-block(179,2)

But then I found this post:

https://raspberrypi.stackexchange.com/questions/40854/kernel-panic-not-syncing-vfs-unable-to-mount-root-fs-on-unknown-block179-6

I wasn't able to boot my raspberry pi by holding the shift key, but I do have another computer running ubuntu. So, i put the sd card in there and manually edited the cmdfile.txt file as described in the post.

However, I don't know enough about fsck to know if I'm able to run the command safely:
sudo fsck.ext4 -y /dev/mmcblk0p6

When I attempt to run it on my ubuntu computer with the sdcard plugged in, I get a warning about severe data loss if I continue.

Anyways, just wondering if anyone has any suggestions on how to fix this? Info about my setup:

Raspberry Pi 3B
Using a Canakit power supply
Unsure whether it's running RetroPie version 4.1 or 4.2 (can't boot up to actually find out)
When I install Retropie, I downloaded from here: https://retropie.org.uk/download/ and used the version 2/3 image.
USB devices: external hard drive, wireless keyboard, usb key
Controller used: 8bitdo nes controller

Can anyone help?

[Hex]

Looks like your SD card is failing. You could either format the entire card and try booting or run the fsck commad. I dont think you have the correct drive. Try checking using Disks utility what is the drive "mmcblk0pX" You need the correct X. If you havent modified partitions then it should be 2

So once you have X you can try this command replacing X with what you got.

sudo fsck /dev/mmcblk0pX

This will tell you the status of your partition.

[jplank]

@Hex IS there a way for me to access any save states that I have on the card in order to back them up? I think that formatting and reinstalling Retropie might be the easiest choice but I don't want to lose my data.

Can you give me more details about how to use the Disks utility? Is this something that has to be run from my Raspberry Pi? Or can I plug the sd card into my Ubuntu computer and run the utility on there? Same question for the sudo fsck /dev/mmcblk0pX command - is that something that I can run from my Ubuntu computer with the sd card connected without causing problems?