This is what I saw, or something similar, after the nurse or technician explained things to me. I don't recall details of exactly what the thing looked like. Well, I had to remove my glasses, so everything was sort of a blur. But this is an example of an MRI machine.
Image from Wikipedia
I tried to measure time, too. The tech had said it would take 20 to 25 minutes. I was pretty close when everything went quiet, and she pulled me out of the monster, my neck scanned.
So, my lesson is don't worry about what might happen. Relax, listen to good music, and pray a lot.
Have you met the MRI machine, or others that weren't nearly as scary as you thought?