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Ah, I think I get it now. Sounds like you are setting the bracketing (AEB), but then firing off the shots in one-shot drive mode instead of continous multiple shot mode. So you press the shutter button and get one shot (+0 exposure), then press the shutter button again and get the +2 exposure, then stop and try to adjust exposure for the 3rd shot (-2 exposure)?
Probably not the best technique. Use multi-shot continous drive mode, press and hold the shutter button and let the camera fire all three shots as fast as possible. When AEB is set, the camera will stop after 3 shots. If AEB is not set, the camera will keep firing shots as long as you hold the shutter button.
If you really want to adjust exposure separately, don't use AEB or continuous drive mode. Just set a manual exposure, fire one shot, adjust the manual exposure (add 1 to 3 stops) and fire one shot again, and keep going until you has as many exposures as desired.
Problem with that technique is that touching the camera to adjust each exposure can cause slight alignment shifts, even with a very sturdy tripod. Plus, the time it takes to do this can result in movement of the subject. It can take 5 to 10 seconds to manually fire bracketed shots, and in that time clouds, trees, water can move enough to cause significant ghosting in the result.