trying to recompile .img using make_ext4fs need help

Hello,

I compiled aosp for my nexus 7 2013 works fine, but i wanted to add apps and tweak things like bootanimation.zip and remove things like email app, i don't use it why waste space. I use the the follow to allow edits

simg2img system.img system.img.raw
mkdir system
sudo mount -t ext4 -o loop system.img.raw system/
I add my edits and than use this but get and error

user@user:~/Downloads/imagedisassemble$ sudo ./make_ext4fs -s -l 512M -a system mesystem.img system/
Creating filesystem with parameters:
Size: 536870912
Block size: 4096
Blocks per group: 32768
Inodes per group: 8192
Inode size: 256
Journal blocks: 2048
Label:
Blocks: 131072
Block groups: 4
Reserved block group size: 31
error: do_inode_allocate_extents: Failed to allocate 3 blocks
I have tried to change 512M to 600M it will finish without error, however when I flash with fastboot flash system system.img, I get stuck on the Google screen and have to force off with power and get into bootloader to try again.

Any help would be great

Thanks
Tony