The bigger blood vessels begin to form around 5 weeks, though obviously there is blood flow to the embryo as soon as implantation is complete (implantation is a gradual process, roughly around 7-10 days past ovulation), which would be before you knew you were pregnant.
Though of course one never knows, honestly I don't think one drunken night at that stage is a big deal at all, and I had one of those right around the time of implantation in my first pregnancy (think many drinks, no dinner). Interestingly, I think it may actually have something to do with the success of that pregnancy. It was my first natural cycle, on metformin, following several failed IVF cycles in which good embryos failed to implant. Much later (as in a couple years later) I found out I have a clotting issue, and alcohol is a blood thinner of sorts. So I think it may have "helped" LOL. (I know everyone probably thinks I'm crazy, but when we were trying to conceive again down the road I set up a little program for myself of a half a glass or less per night of wine during the implantation timeframe and it worked both times I tried it).
So, nah, I wouldn't worry. Congratulations!