Your problem is a common one that I also had and has been explained elsewhere on the forum somewhere.
You're using Rewritable disks and the standard size format is smaller for a rewritable disk than a write once disk. This only applies to Blu-ray disks, not DVD or CD.
Rewritable disks are formatted with a safe area so they show up smaller. Use ImgBurn to format the disks and under the tools-->settings menu select the write tab. On the right where it says 'prefer format size' change it to Maximum. Also check all three 'prefer' boxes above it. Now when you format your BD-RE and BD-RE DL disks they will end up with the same number of sectors as a BD-R disk and the same size. DL disks will now be 50 gig instead of 45 gig.
That's why DvdFab has different setting in the writable media size for blu-ray.
It takes forever for ImgBurn to format, which is why I only do that when I need one that size (cloneing 3d blu-ray). If you erase the disk with most quick format programs, it will default back to the smaller size with the safe area.
It's a pain, but I always verify first on a rewritable before a write once. They are too expensive to waste.
