Can't mount an image created by ddrescue

I have a 500GB disk that I'm trying to recover using GNU ddrescue.

This is the fdisk for the 500GB disk:

Disk /dev/sdc: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 33553920 bytes
Disk identifier: 0xeea5da13 Device Boot Start End Blocks Id System
/dev/sdc1 63 976768064 488384001 7 HPFS/NTFS/exFAT

ddrescue completed its copying run and was doing this:

GNU ddrescue 1.21
Press Ctrl-C to interrupt
Initial status (read from mapfile) rescued: 481966 MB, errsize: 70382 kB, errors: 121
Current status ipos: 482180 MB, non-trimmed: 0 B, current rate: 262 kB/s opos: 482180 MB, non-scraped: 17927 MB, average rate: 614 kB/s
non-tried: 0 B, errsize: 70382 kB, run time: 3m 54s rescued: 482110 MB, errors: 121, remaining time: 1d 10h 58m
percent rescued: 96.40% time since last successful read: 0s
Scraping failed blocks... (forwards)

The step above is now complete, and this is what fdisk -l says on the backup.img file:

Disk /media/victor/New Volume4/backup.img: 497.3 GB, 497334280192 bytes
255 heads, 63 sectors/track, 60464 cylinders, total 971356016 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xeea5da13 Device Boot Start End Blocks Id System
/media/victor/New Volume4/backup.img1 63 976768064 488384001 7 HPFS/NTFS/exFAT

When I do sudo mount -o ro,offset=$((512*63)) backup.img /media/myName/recovery I get:

Failed to read last sector (976768001): Invalid argument
HINTS: Either the volume is a RAID/LDM but it wasn't setup yet, or it was not setup correctly (e.g. by not using mdadm --build ...), or a wrong device is tried to be mounted, or the partition table is corrupt (partition is smaller than NTFS), or the NTFS boot sector is corrupt (NTFS size is not valid).
Failed to mount '/dev/loop0': Invalid argument
The device '/dev/loop0' doesn't seem to have a valid NTFS.
Maybe the wrong device is used? Or the whole disk instead of a
partition (e.g. /dev/sda, not /dev/sda1)? Or the other way around?

What do I do now?