First full backup on USB: Permission denied

You need to set ownership & permissions.

https://help.ubuntu.com/community/FilePermissions

If mounted at /media/stacyjane

sudo chmod -R a+rwX,o-w /media/stacyjane
sudo chown -R $USER:$USER /media/stacyjane

Note that the -R is recursion and everything is changed, do NOT run on any system partitions. All directories will be 775. All files will be 664 except those that were set as executable to begin with.

The -R parameter is recursive, so it will apply to all lower directories & files, but do not use on any system partition, just data.

see also

man chmod
man chown