EC2 instance failing status check due to full disk

I have an Ubuntu instance created from a marketplace AMI, and it's failing status checks after a reboot. System logs show this:

[ 99.747391] cloud-init[864]: OSError: [Errno 28] No space left on device [FAILED] Failed to start Initial cloud-init job (metadata service crawler). See 'systemctl status cloud-init.service' for details.

I increased the volume size, but it seems to be failing before it gets to the point where it's able to extend the filesystem. I don't have a password-enabled user, so I can't use the serial console. I spun up a temporary instance and tried to mount the root volume as a secondary volume, but got an error because it's from a marketplace AMI. I launched a new instance from the same AMI, but am still unable to mount it. Do I have any other options?