[CentOS] USB of ISO image

I copied the 7.7 Everything ISO to a 16G USB device using dd. I mounted
/dev/sdb2 and edited grub.cfg for my custom install option.
I then ran the command below to re-do the boot menu. the command runs ok -
However it did not work.

cd /mnt/usb/EFI/BOOT
grub2-mkimage -o bootx64.efi -p /efi/boot -O x86_64-efi \
  all_video boot btrfs cat chain \
  configfile echo efi_gop efi_uga \
  efifwsetup exfat ext2 fat \
  gfxterm gfxterm_background gfxterm_menu \
  hfsplus iso9660 linux loadenv \
  loopback ls lsefi normal ntfs \
  part_gpt part_msdos search search_fs_file \
  search_fs_uuid search_label test udf usb


I do not see my new menu option.

How do I correctly re-do the grub boot menu on the USB device.

Thanks,

Jerry