I remember the time I was among a group of girls and I was the only guy.
Throw in a few jokes, lead the conversation, everything will be alright eventually.
It might be hard for a few people but just remember that the first impression matters here. If there's even a slight bit of awkwardness at the start, everything is ruined. Just be relaxed, if you can make yourself look comfortable then you'll have a lot of chances to join in naturally later.