The first one I had, back in the 1990s in a travelling one, was horrible because I was sealed in a sort of cigar tube and I'm a bit claustrophobic.
However, be of good cheer, it's nothing like that nowadays. I had 2 in France and they were perfectly pleasant, no problem at all - tube open both ends and plenty of headroom.
I've had a full body MRI since returning to the UK (MRI about 5 yrs ago) and it was a bit in-between. My face was much closer to the machine's surface and so it was much more claustrophobic (only a couple of inches between my nose and it). The removal of a pillow rendered it much more tolerable.
It's nothing to be worried about. I won't worry if I have to have another.