Installation doesn't register full amount of available storage space and I can't update / install anything new

I recently installed CentOS(7) on a Raspberry Pi 3B with a 32GB microSD card. When I tried to install new packages or update, I got an error saying that there wasn't enough space in the root / main directory. I typed "df -Th" and saw that the full 32GB storage capacity wasn't being used or recognized for whatever reason, and that the "/" directory was only 1.7 GB. The numbers listed don't add up, and I'm not sure I understand why the OS won't recognize / list the rest of the available storage space. What dumb mistake(s) am I making here? *screenshot attached*
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