I felt like this for a long time. Honestly, you might never have a big group like some of the girls - some people just don't work that way socially. That doesn't mean you can't have an awesome experience, though. Start small - hang out one on one with a few of the girls that you're closest with, start by getting lunch with them and such, and then start inviting them out in small groups if they get along with one another. I don't really have a "group" within my chapter, but I've gotten to be super super close with a few sisters individually. Not everyone is going to have the same experience, and that's okay.
I also recommend taking a little, if you can
