I'm also going to be slightly blunt here - but this is coming from someone who has life limiting illnesses for which i have absolutely no choice about whether I have invasive and unpleasant procedures, scans, imaging, tests constantly.
You either get the MRI or you don't. Go to your GP and ask for some meds to cope with it, but winding yourself up now is just going to make the whole situation worse.
You've got a choice - get the MRI and hopefully you'll be further along the way to getting any medical help or treatment you need, or don't get it. And then you won't be able to get that help.
Sometimes we have to do things we don't like doing and this is one of those times. If the benefit of a diagnosis / something being monitored and treated is outweighs the unpleasantness of having the MRI.. you'll just need to suck it up.
There's no risk to you whatsoever in having it done. It can't hurt you and nothing can go wrong, so as medical procedures go that's pretty good as there's no possibly way you could be adversely affected.
So it's your choice, no one is forcing you, but if you want the over all situation to improve, then you need to get some help from your GP, and just get through it, otherwise you're stuck.
Winding yourself up on MN where other people are going to make things worse by saying how much they hate them as well, and confirming your fears, likely is just going to make things worse.
Sorry for being blunt but you just have to ask for some help and get on with it.