fsck still going 24 hours later

I have a 1TB NVMe with Ubuntu (~300GB used). Using a live USB + GParted, I resized the root partition to 400GB.

When I rebooted I got the error "File system check of the root filesystem failed. The root filesystem on /dev/... requires a manual fsck" (something like that, I don't remember exactly). So I ran fsck -fy /dev/... and it's been going for a full day now.

Right now it's doing tons of these: "Unattached inode ####. Connect to /lost+found?", but earlier it was something with deduplicating blocks that were used by multiple inodes or something.

Does anyone know what's happening? Did I do something wrong? How long could this conceivably take for 300GB of data? Is it possible to safely interrupt it?

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