how do I stop ChatGPT from making things up?
You can't stop ChatGPT from making things up completely, but you can cut it hard: use your actual source instead of asking from memory, give it permission to say “I don't know,” and ask it to quote its basis.
Interactive: watch ChatGPT invent a confident, specific fact — then paste the real source, give it permission to say “I don’t know,” and ask it to quote its work. Fabrication drops. It never hits zero.