Extended an encrypted partition, why the disk space is unused?
Immediately (no reboot!) backup your main volume with Time Machine to an external volume.

Boot to Internet Recovery Mode, erase your disk and restore the backup.



Your Recovery Partition (size: 41509000 blocks/21.25 GB, index 3) seems to be hosed but holds some invisible intermediate encryption/decryption keys for your encrypted  main volume. Usually this partition is much smaller (size: 1269536 blocks/650 MB) and has a different ending block. So the boundaries of the Recovery Partition may have been moved without moving the content of it. Consequently it's saver to backup and restore! 

Unless you don't reboot this is no problem.