You can't go back in time, so the first thing to do is stop worrying.
There is some research to suggest that a few drinking sessions (that were not too excessive) are not going to affect the baby in the long run.
Some women find that they get more unexpectedly sick after a few drinks anyway, even if they don't at that point know they are pregnant, and this inadvertently curtails their drinking.
Even if you have had a binge, you cannot change the course of history now so it is better to start thinking about getting together a good basis for pregnancy diet and nutrition from here on in.
Alcohol in your system
Anyone who has ever had an alcoholic drink will tell you that it has an effect on the brain and body. Because these effects are transported through the blood stream, and a fetus takes all its nutrition directly from the mother's blood, it is easy to see that continued drinking through pregnancy would have a negative effect on the baby.
The odd drink of wine or lower alcohol beer will not neccessarily be a worry, but continued heavy drinking on a regular basis has been shown to affect a baby's brain and physical development.
Nine months without booze
If you find that you really miss your glass of wine at the end of the day, check out this ThinkBaby article on booze-free alternatives. Remember, too, that even soft drinks can be full of unpleasant additives like saccharine. The Food Standards Agency offers safe guidelines on food and drink during pregnancy and recommend a maximum of one or two units of alcohol twice a week, as a maximum during pregnancy.