Maybe you can ask how long your MRI is expected to take? I had two MRI’s one day apart, and the first was a pelvis MRI to check m y fistula, and it only took 15 minutes! I was in and out so fast! The 2nd was a bowel MRI and it took much longer, about 45 mins. If it’s for your pelvis it might be a quick one.
Also, as the others have said, you are given a panic button to squeeze if things get hairy for you….. and your head will probably be poking out of the hole at the top, so the only thing in a confined space is your body, and even that has room to move, its not like a coffin!
Hope all goes well, I’m sure it will be less scary than you anticipated, just remember, its all in the mindset!