Hey .

Try
which fdisk
or
which sfdisk
or which gparted

and see, if you have them installed.
Output should be
/sbin/fdisk
or similar.

Then you may try to get your first partition back and restore also the file system flag. Maybe you are lucky and MyDocs is as before.

If not, you may reflash your device with eMMC vanilla image first. no reboot and then flash firmware.
This will for sure recreate everything and you will have a virgin N900 again.