Thinking you are being kidnapped is a mistake. But if you have a firearm, you can rectify that by just saying “I have a firearm, stop the vehicle and let me out please.”
I think about 99.99% of people, even those with criminal intent, would probably comply.
Just ask to be let out. If they don’t make a motion to pull over and end the ride within a reasonable period of time, then you brandish the weapon and call the police.