If he made it clear that he was going to use force if you said no, yea.
Maybe we should not say no.
Everything depends on context, how well do you know this person? If you know he is a serial rapist it might not be worth the risk to refuse at all.
If it is a stranger, and I think that is the scenario, then chances are polite "no" is going to work 99%+ of the time, it's a safe opening move.
If you don't say no at any point and no threats are made you're (objectively) consenting, so at that point you're just saying you're so afraid of the <1% chance of being raped that you decided to actually consent. Up to the individual, but it casts no blame on the stranger.
BUT pretending to change your mind is the best strategy to live to tell the police.
This would be a lie. A man would be able to tell it isn't real.
Oh naivete is thou name.
Some rapist are turned on by lack of consent, consenting would turn them off or they would try to make it painful. No hope there.
Others are delusional, constantly revising history and the present to convince themselves that the other person wants it. <- That's who you'd be fooling, and it wouldn't take great acting skills it's what they want to believe so badly they're out of touch with reality.
What would you tell the police if you don't know his name or have license plate? “A man in the forest raped me, but I pretended to change my mind. I have no idea what his name is or where he is from.”
Well even if you can't get justice, you survive. Like ratman said, DNA is possible but wouldn't be enough to prove anything. Still making reports is important for context in future suspicion.
It's also much more likely you can get justice yourself (kill the guy) if his guard is down.