I think the first step would just be to call your doctor's office after hours line if you're that concerned. But I can't imagine that one advil would hurt the baby.
I'm with @kristen2b - I think you'll be okay with one Advil. I'm sure you're not the first pregnant woman in the world to forget the rules for a minute!
Re: HELP !!
https://www.motherisk.org
Side note:we call our crew "macattack"