Congrats! Definitely give it some time - you might have more in common with your pledge sisters than you think. Everyone's emotions are on such a roller coaster during rush that sometimes when you step off, you still have that woozy, I need to barf feeling!
Even if you don't turn out to be super close to your pledge sisters, I wouldn't let it stress you out - it's not a law that you can only be close to people in your pledge class, and none of my best friends from my sorority pledged with me.