My recommendation for tonight is to not focus on asking questions about the sorority. I would just focus on having a real conversation with the girls and getting to know them (and letting them get to know you). This way they can really see how you will fit into their chapter. Others may not agree with me, but I personally think that that will have the most impact on the chapters.
As for being a minority- OF COURSE they will still want you! If you are offered a bid from either of these chapters, know that it is because they saw something special in YOU that they want in their sisterhood- not your race. Also know that if by some chance it doesn't work out, it is also not because of your race. Sometimes things like that just happen.
I think that you are doing everything you need to be doing. You are obviously very enthusiastic and the chapters will notice that. So, tonight just focus on being yourself and getting to know the ladies you meet. Things will end up the way they are supposed to! Keeping my fingers crossed for you!
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