It isn't really all that bad, you have added 1kg more dextrose than planed.
Without more information I'm only guessing but lets say you are doing a "standard" 23L batch.
1kg of dextrose will only add 910g of fermentable that means about 0.0156 of extra gravity, that is about 2% more alcohol than planed.
Suggestions! - meh it wont affect the flavour too much, just pay attention next time and drink with caution.
Don't know where you get the idea that waiting will bring the alcohol down, that isn't generally the case, well unless its an open fermenter that really hot (say >78oC).
There are plenty of other things you can do, like make a lower alcohol beer and blend... but it probably isn't worth it in this case.
Mark
PS - Love the avatar
m