What if I'm not offered a bid in either my top 2?

If you mean pref, you are guaranteed a bid to one of your pref chapters if you rank both of them on your card. If you only have one invite for pref and put them on your card then you are guaranteed that bid. BUT, if you have two prefs and only list one then you would only get a bid if you were high enough on that one chapter's bid list to match with them before they reach quota; if not then you would not get a bid.

But also you need to adjust your expectations if you think that this is all about your choices and that you just go through rush getting back your top ones each round. It's up to the sororities who to invite, and your top choices may like you just fine but if you aren't high enough on their list to make their cutoff for any round then you are released from their recruitment. Hopefully you will be excited about who you have for pref because they are the ones who want you and all sororities are good here. But the ones you get invited back to each round may not be the ones you thought you wanted or were expecting at the start of recruitment. Keep an open mind.