This is because the image-full-galileo.ext3 on your SD card is 302MB. This is the root partition.
Now there are two options that can be done.
1. Try changing IMAGE_ROOTFS_SIZE in the image-full-galileo.bb file before you bitbake.
2. Mount your SD-card, Next mount the ext3 rootfs on the loop device.
Create a new ext3 with the specified size on your harddisk and copy all the files.
Now copy this new ext3 to the SD-card replacing the old rootfs.
Let me know if you need more detailed instructions,.