I was dead nervous for nothing! Even with a previous overstay (of 5 days) and a denial of entry at LAX I was approved for my K1 in Sydney. I just made sure I told the utmost truth in what happened and why.
She didn't really ask me much about my fiance all that much, as I had a sworn statement with US immigration talking about our relationship. Her questions mostly focused on my overstay. I hope this helps anyone with previous run ins with border protection.