Everyone makes mistakes in interviews. Recovery matters more than perfection.
You realize your design is flawed: "Wait, I see a problem. This won't scale because X. Let me revise." Shows self-awareness.
You don't know something: "I'm not familiar with that specific technology. Here's what I'd expect it to do based on similar systems."
You're stuck: "I need a moment to think through this." Silence is okay. Rambling isn't.
Never pretend to know something you don't. Interviewers detect BS instantly.