Need some advice...

So I just found out I was pregnant over the weekend. I am going to a wedding in a few weeks and there will be an open bar. My best friend has been talking about nothing but getting drunk together (since I very rarely drink and its been forever!!) I want to try and wait to tell my family and friends till I hopefully find out the sex (my family doesn't like my boyfriend and we already have two boys. So I'm hoping it's a girl so make them happy for my pregnancy) How can I go about avoiding to drink without having to straight up tell them I am pregnant?? I'll be about 6-7 weeks when I go to the wedding.