dheianevans; Hi !
du is not lying to you, arithmetic: 491 is to 454 as 100 (%) is to "x" = 92.46, less than 8 percent remaining, root may take another 5 percent... you do not have overhead left to operate with. You need to do some trimming. Done any house cleaning lately ?
I suggest you start with /var/log/ ... one may safely delete any file ending in .gz located in any of the folders within /var/log/. May gain you some significant amount of space.
then there is also orphaned and obsolete files:
You sdb5 storage partition is also running short on room.
sudo apt-get autoclean
sudo apt-get autoremove
sudo apt-get clean
just try'n to help <==BDQ