Ubuntu on Beagleboard C3 - unable to boot

[Apologies if this is a duplicate post: not sure if the prev attempt worked]

Hello all,

I wanted to put Ubuntu on my beagleboard Rev C,
and I followed the instructions here:
I’m doing all this with a desktop running Ubuntu 14.04,
on which I cross compile the kernel.

The instructions are quite good, and everything seemed was going as expected.
I successfully compiled the 4.6 kernel without any errors.

In the ‘prepare SD card section’,
however, i noticed that the command given creates a /rootfs partition of just 1MB.
The boot partition is 12MB, which seems ok.

Naturally /rootfs was too small, so I created another 4GB ext4 partition, using that instead of the original
1MB partition. To account for this I changed the fstab, to mount the new rootfs (mmcblkp3) on /.

Then, pressing down the user button, I powered up the Beagleboard.
I get messages on the serial port, the last of which is “starting kernel…” - and nothing more.
The full bootup message log is here: http://pastebin.com/raw/x1izWrk

The log shows:
Loaded environment from /boot/uEnv.txt
Checking if uname_r is set in /boot/uEnv.txt…
Running uname_boot …
loading /boot/vmlinuz-4.6.1-armv7-x4 …

which means the rootfs partition is being read properly,
but how do I know the correct partition is being mounted?