Ok ok... now I see why...
So you problem is that you have a extremely bring background and you try to fill you subject using a flash.
When you use a fill flash, the flash will usually just illuminate the subject and not the background. The balance fill-in programme in your SB-800 will normal do the job very well in the TTL/BL mode.
It is very unlikely that you use the flash and still have the background +3EV overexposed unless you have having a extremely bright background and a super weak flash. (For theoretical discussion, ExplorerZ is right, but practically that should not happen.)
When flash is used, the tendancy is that you have a very bright subject and a dim background which looks unnatural. You will normally need to do some exposure compensation to get the balance between the subject and background. Usually you do a +ve exposure compensation and a -ve flash exposure compensation.
I have yet to encounter a situation when I use flash and I do exposure compensation the other way around.
BC