Fedora uses LVM as default "partitioning" method. The /dev/sda3 is LVM Physical Volume and it cannot be mounted. You have three (at least default installation create three) LVM Logical Volumes used for / (you can see /dev/mapper/fedora-root mounted at /), /home (I don't see it in /proc/mounts you provided) and swap (/dev/mapper/fedora-swap visible in fdisk -l output). If you want to see list of logical volumes, you need to use LVM commands -- lvs for logical volumes, pvs for physical volumes (you have just one PV -- /dev/sda3 and vgs for volume group (you have just one VG named fedora).
Fedora uses LVM as default "partitioning" method. The /dev/sda3 is LVM Physical Volume and it cannot be mounted. You have three (at least default installation create three) LVM Logical Volumes used for / (you can see /dev/mapper/fedora-root mounted at /), /home (I don't see it in /proc/mounts you provided) and swap (/dev/mapper/fedora-swap visible in fdisk -l output). If you want to see list of logical volumes, you need to use LVM commands -- lvs for logical volumes, pvs for physical volumes (you have just one PV -- /dev/sda3 and vgs for volume group (you have just one VG named fedora).
Fedora uses LVM as default "partitioning" method. The /dev/sda3 is LVM Physical Volume and it cannot be mounted. You have three (at least default installation create three) LVM Logical Volumes used for / (you can see /dev/mapper/fedora-root mounted at /), /home (I don't see it in /proc/mounts you provided) and swap (/dev/mapper/fedora-swap visible in fdisk -l output). If you want to see list of logical volumes, you need to use LVM commands -- lvs for logical volumes, pvs for physical volumes (you have just one PV -- /dev/sda3 and vgs for volume group (you have just one VG named fedora).