There are loads of people who drink before they knew they were pregnant - if people didn't get drunk, there probably wouldn't be as many babies born anyway ;o).
As my doctor said to me, obviously you should do your best to stick to the medical guidelines, but the stress of worrying about something you may have done will be worse for the baby than whatever it was, so you need to chill and relax.
The chances of anything being wrong are minute.
The main reason that you should follow the rules now is that if there happened to be anything wrong, even if that was absolutely unconnected, you would blame yourself.
If you are concerned, chat to your doctor or midwife about it - I can guarantee that it will be a familiar story to them and that they will be able to put your mind at rest.