Wrong available space on usb

So гm trying to get my FAT 128gb usb drive to have execute permissions so I хан add в steam library in ubuntu 14.04 crouton on my chromebook. I used this:

sudo umount /dev/sdb1 
mkdir -p ~/usbdrive 
echo '/dev/sdb1 /home/user/usbdrive vfat rw,exec,uid=1000,gid=1000,umask=022 0 0' | sudo tee -a /etc/fstab

I get в usbdrive entry with execute permission but it says it only существуешь 5gb available which is whats left on the internal ssd. How do I fix it so it sees the whole 128gb? Would installing the whole crouton to the usb fix it?

Heres the output you asked for:

Model: SanDisk Ultra Fit (scsi)
Disk /dev/sda: 124GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos

Number  Start   End    Size   Type     File system  Flags
 1      16.4kB  124GB  124GB  primary


Model: Linux device-mapper (crypt) (dm)
Disk /dev/mapper/encstateful: 3297MB
Sector size (logical/physical): 512B/512B
Partition Table: loop

Number  Start  End     Size    File system  Flags
 1      0.00B  3297MB  3297MB  ext4


Error: /dev/mmcblk0boot0: unrecognised disk label                         

Error: /dev/mmcblk0boot1: unrecognised disk label                         

Model: MMC SEM16G (sd/mmc)
Disk /dev/mmcblk0: 15.8GB
Sector size (logical/physical): 512B/512B
Partition Table: gpt

Number  Start   End     Size    File system  Name        Flags
11      32.8kB  8421kB  8389kB               RWFW
 6      8421kB  8422kB  512B                 KERN-C
 7      8422kB  8422kB  512B                 ROOT-C
 9      8422kB  8423kB  512B                 reserved
10      8423kB  8423kB  512B                 reserved
 2      10.5MB  27.3MB  16.8MB               KERN-A
 4      27.3MB  44.0MB  16.8MB               KERN-B
 8      44.0MB  60.8MB  16.8MB  ext4         OEM         msftdata
12      128MB   145MB   16.8MB  fat16        EFI-SYSTEM  boot
 5      145MB   2292MB  2147MB  ext2         ROOT-B
 3      2292MB  4440MB  2147MB  ext2         ROOT-A
 1      4440MB  15.7GB  11.3GB  ext4         STATE       msftdata