Seconded, ready, you and baby will be fine. As Wispa said, the flow of nutrients through the placenta doesn't start until 5-6 weeks. And although drinking heavily in pregnancy is undoubtedly harmful, less crosses the placenta than you think as your liver metabolises a lot of it before it even gets to the placenta. Not that I'm advocating drinking during pregnancy, but FASD usually occurs when the mother drinks heavily repeatedly during pregnancy, not one weekend of drinking at 4 weeks! I read up on all this during my first pregnancy as I liked to be informed about why the guidelines around food, drink, medication exist.
P.S. I had a few drinks at the weekend too, if that makes you feel any better!