Meeting the family

I'm stressing. I'm meeting my boyfriends entire extended family today because his mom (who I haven't met yet) invited me to their family holiday party.

I'm super nervous. We've only been dating for a month and the only member of his family that I've met is one of his older sisters.

I feel like it's going to be way too much at once considering he has like six siblings and who knows how many aunts/uncles/cousins there. My parents have already met him and they adore him. I really want his family to like me too.

Edit: Also his mom's side of the family is from Britain and mine's from the US. I hear they're more strict about manners there? I'm just so scared of messing up.