@aromano Ah. I didn’t realise you were booting from an external USB.
If I remember correctly, the script that expands the resin-data partition does not expand the partition on externally plugged usb drives.
If its easy for you, plug out the usb, expand the resin-data partition to fill the rest of the disk using a tool like gparted.
Alternatively, you can do this on the device itself. There are some instructions here for the pi3. But they should be applicable to the NUC as well. Raspberry to run resin.io from Hard disk
Regards
ZubairLK