Are you actually using R28.1? If using R28.2+, then you have some prebuilt example gadget set up (and the instructions for R28.1 might be interfered with when trying to run at the same time as the R28.2+ sample).
If you download the R28.2 driver package, and then unpack it, you will find this:
If you unpack that in an empty directory somewhere you will specifically see content in this directory (or if you are running R28.2+ this will already exist on your TX2):
If you run the script “nv-l4t-usb-device-mode.sh” as root (e.g., sudo), then this will set up various sample devices. Keep in mind that the emulated hard drive depends on the filesystem.img being there. If you don’t want to create a fake ethernet device, then you can comment it out in “nv-l4t-usb-device-mode.sh”. Comments in the file should help understanding it even if you’re not using that file. You should be able to copy that content to an R28.1 TX2 and have it work (assumes gadget is configured in the kernel…which it might already be done even by default on R28.1).