fill

ok on a bright sunny day and you want to use fill flash.
the flash speed is 250 correct?
if I don't change the aperture then i will blow the highlights correct?

so i have it set at 2.8 at 1/4000 in av this going to make the picture way to bright.

hope this makes sence

Yep.

If you set your shutter speed at 1/4000 but use flash, the camera will shoot at 1/250 and blow out the shot.

So you have a few options:
1) Stop down the aperture (your ISO should be at 100 already), or use Tv mode at 1/250 shutter speed and let the camera select the aperture.
2) Use high speed sync, which enables faster shutter speeds but reduces your effective distance.
3) Use a polarizer or ND filter in combination with #1 above, if you desire a wider aperture for less DOF.

Sunny 16 rule says 1/ISO shutter speed with f/16 aperture...1/100 f/16 for ISO100.
You could change this to 1/200 f/11 and still avoid the HSS mode and its loss of max range for the flash when in HSS with shutter faster than 1/250. Assuming f/11 on the lens, and assuming a flash with a Guide Number of 110, you could still have the flash provide fill at -1EV less intense than the ambient light out to a range of 14 feet (110/8 = 13.75).