It's highly unlikely the beer will affect your pregnancy. With my first I told my doctor that I had A LOT (and I mean A LOT) to drink the weekend before I found out I was pregnant. I had also been drinking my regular amount that entire month -two or three nights a week with two or three drinks. The weekend before I found out I was pregnant my husband and I celebrated our 5th anniversary. Friday night was spent at an opulent dinner and a hotel where bottles of wine and champagne were consumed as well as some house-infused vodka at the restaurant. Saturday night we threw a huge party at our house and I drank these special rum concoctions I came up with just for that evening. I also smoked about two packs of cigarettes that weekend!
With the second baby, the night before we officially decided to "try" again, we had about 3 bottles of wine -and again -a lot of cigarettes. The next morning it dawned on me I should have gotten my period and whoops -I was already pregnant! Both children are perfectly fine and wonderful!
My OB GYN told me with the first that if she even had a nickel for every woman who told her she had gotten drunk, smoked pot, been drinking heavily, etc. before finding out she was pregnant, she would have retired a long time ago! OF course that's finding out you're pregnant within a normal amount of time -not at 5 months or anything. As long as you quit drinking the minute you find out, everything should be okay!