Teaching it to say "I do not know"
Why refusing is a feature, and how to make refusals useful.
Keep Only answer from my material switched on. That is the setting that stops invention. With it on, a question outside your material gets an honest refusal rather than a plausible fabrication.
Make the refusal do something
A dead-end "I do not know" wastes the conversation. Use the Always mention field on the Guardrails step to give it somewhere to send people: book a call, join the list, email you.
Refusals tell you what to write next
Every refusal is a question someone had that you have not covered. Check your Conversations regularly and turn the repeated ones into Q&A entries.
This is the loop that makes a clone better over time, and it costs about ten minutes a week.
When it refuses things it should know
That is a knowledge problem, not a guardrail problem. See "Your clone does not know something you uploaded" before you consider turning the guardrail off.