I have a similar problem trying to shrink my image with pishrink.

pi@pi-VirtualBox /media/sf_SD__images $ sudo ./pishrink.sh 64gb_Papberry_arcade.img
[sudo] password for pi:
tune2fs: Attempt to read block from filesystem resulted in short read while trying to open /dev/loop0
Couldn't find valid filesystem superblock.
tune2fs: Attempt to read block from filesystem resulted in short read while trying to open /dev/loop0
Couldn't find valid filesystem superblock.
mount: /dev/loop0 is write-protected, mounting read-only
mount: /dev/loop0: can't read superblock
md5sum: /tmp/tmp.JImqrA1mnE/etc/rc.local: No such file or directory
./pishrink.sh: line 63: [: !=: unary operator expected
umount: /tmp/tmp.JImqrA1mnE: not mounted
e2fsck 1.42.13 (17-May-2015)
e2fsck: Operation not permitted while trying to open /dev/loop0
You must have r/w access to the filesystem or be root
resize2fs 1.42.13 (17-May-2015)
resize2fs: Operation not permitted while trying to open /dev/loop0
./pishrink.sh: line 136: [[: Couldn'tfindvalidfilesystemsuperblock.: syntax error: invalid arithmetic operator (error token is "'tfindvalidfilesystemsuperblock.")
expr: syntax error
expr: syntax error
expr: syntax error
resize2fs 1.42.13 (17-May-2015)
resize2fs: Operation not permitted while trying to open /dev/loop0
Couldn't find valid filesystem superblock.
ERROR: resize2fs failed...
mount: /dev/loop0 is write-protected, mounting read-only
mount: /dev/loop0: can't read superblock
mv: cannot stat '/tmp/tmp.JImqrA1mnE/etc/rc.local.bak': No such file or directory
umount: /tmp/tmp.JImqrA1mnE: not mounted

@mitu running the command you said, this is the output:

pi@pi-VirtualBox /media/sf_SD__images $ parted -m 64gb_Papberry_arcade.img unit B print
WARNING: You are not superuser. Watch out for permissions.
BYT;
/media/sf_SD__images/64gb_Papberry_arcade.img:64021856256B:file:512:512:msdos::;
1:4194304B:63963135B:59768832B:fat16::boot, lba;
2:63963136B:63864569855B:63800606720B:ext4::;

(I don't know how to use the forum editor to make this code looks like yours, with black background)