Chemistry ranks about... last, on our list of admitted criteria. It's just as obvious to us as it is to you, that not everyone will have chemistry with each other. We're not running popularity contests here- the interview sheet does not say, 'will you want to be this guy's friend?'
That aside, having a script is the worst thing you can do. There are many stories here in the admissions office of interviewers realising within 5 minutes that there was a script, and then they were just waiting for time to end. BTW, when there is a script, interviewers tend to 'challenge' a bit, and then give up. So, them continuing to challenge you might not be a bad thing. It might indicate they're engaged, and it might mean they're giving you a chance to shine.
Although I admit, it could also simply be that they're not convinced you're good candidates.
Regardless of which it is, it is my experience from interacting with close to a hundred applicants now who are right about to go into the interview, that many of them are so nervous that they can't properly judge what others are thinking/doing. So, don't bother speculating what the other person is thinking. Just relax, convey the story of yourself (and you're the best person to do that!), and you'll be fine!
To sum up, about telling a script, here's what Mark Twain once wrote: "If you tell the truth you don't have to remember anything". If you're trying to memorise a script, what might that imply about whether you're telling the truth?