Alcohol before knowing you were pregnant?

Has anyone been guilty of using alcohol before knowing you were pregnant?? I took a test on the 6th and 9th and both were negative so I was sure I was not pregnant. I went out for my birthday on the 9th and 10th and had about 3-4 drinks each time. Not sure why but decided to take another test on the 12th and it was positive! I want to be oh so excited but I'm feeling overwhelmed with fear and guilt. I'm not sure if I was at the end of my 2nd week or beginning of my 3rd (or 5th going off LMP) but I'm terrified it was the end of the 3rd since that is when all the important neural development starts. Freaking out!! Anyone?