I was a 70+ units a week kind of gal and the night before I did a test completely expecting it to be negative I had a couple of gin and tonics and a bottle of red, ds1 is completely fine and I know lots of my friends who didn't find out until quite late and straight after Christmas etc. Congratulations
When I had DC1 I was only really 'dating' his dad and we thought we were being careful. Effectively we spent our time drinking and erm ... shagging! He was a bar manager and we drank a lot!! I found out at 12 weeks and had been drinking heavily throughout that time and DS is fine. I daren't touch another drop for the rest of my pregnancy. I'm sure everything will be fine.
Try not to worry. It happens to most people apart from those who have sworn off alcohol whilst trying to conceive. I got completely hammered at least 3 times between conception and finding out I was pregnant.
I drank so much in the early stages of preg with DS1, Very "Merry" Christmas, even drunker New Yr & totally pissed up works night out, had done tests before all but all came back neg, It was out with friends for birthday in mid January, i was drinking and someone started smoking and the smell made me feel really sick (id never had that before) went home that night, woke the following day did another test and was pos. turns out i was 9 weeks! He is now 5 and perfectly normal healthy little boy.