You should look at the
Blue Iris Status window > Storage tab to see more information about the disk usage. This stuff is all configured in Blue Iris Settings > Storage tab. You may have allocated too much space and need to subtract about 100 GB from the allocation.
It is also possible that the clip database is corrupted and incorreclty tracking how much space is being used. If that is the case you would need to right click a clip in Blue Iris and choose Database > Delete & Regenerate and then wait potentially a few hours for the database to rebuild (during which time no recording will happen).