Sometimes, things just don't match, it is not a good day, bad hair, etc.
At the end of the interview you might be able to save it with something like this...
“Thanks for taking the time to answer my questions! I’d love to take this final opportunity to reiterate my fit for the position. Based on our conversation, I know you’re looking for someone who knows her way around data, takes initiative, and thrives in a team setting. My three years of experience in economic consulting gave me ample opportunity to really shine in these areas, and I’d love to bring these skills and traits to your company.”
