Dave,
Here are the steps to manually resize your third partition:
Issue the command sudo fdisk /dev/mmcblk0
Hit p then Enter to display your partition table
Take note of the number in the Start column for /dev/mmcblk0p3
Hit d then Enter, you’ll be prompted for the partition number
Hit 3 then Enter
Hit p to verify the partition is gone
Hit n
Hit p You’ll be prompted for the partition number
Hit 3 then Enter
enter the Start number you made a note of earlier
If you want to use the rest of the space on the card, hit Enter, otherwise type +size{K,M,G} e.g. +8G
Hit p then Enter to verify the partition has been created
Hit w to write the partition table
Reboot
Log in and issue the command sudo resize2fs /dev/mmcblk0p3
Done