Good luck, Sarah.
My diagnostic MRI was my first also and I found that if I closed my eyes when I was in the tube and put my mind elsewhere (I was walking on a beach in Hawaii) it wasn't bad. The clanging is a little loud, but you learn to tune it out.
If you find that your anxiety level is high and you just don't think you can handle the tube of gloom (as us old-timers like to call it) you can ask for a mild sedative (Atavan, I think) to help you get through it. There is absolutely no shame in this; lots of people need help to get through an MRI.
Although I don't wish repeated MRIs for you, I have to say that over time I've actually learned to like the tube of gloom. I find it very peaceful, despite the loud clangs, and two years ago I actually started to be able to open my eyes and look around when I was inside the tube.
Hang in there and think good thoughts.
Best,
Jan