I assume this relates to your first post here http://www.thehomebrewforum.co.uk/showthread.php?t=74961
Why post twice?
Anyway if your brew is is already going, and two days on, I can't see any problem in adding the additional fermentables i.e the difference between what you should have added relative to what you actually added. However if the additions includes DME I would not use that, cos its not going to dissolve much, I would add it as LME instead, or at as dextrose which unfortunately will thin your beer.
All that said if I were you I would not be bothering, accept what you have now got, and if you want to consume more alcohol at a session just drink 5 pints instead of 4. :thumb: