When I had my MRI, they gave me ear plugs to wear and insist everyone must wear them. I was glad for them because even with the ear plugs in, it was loud enough.
Like Mark, I'm claustrophobic, so I tuck my elbows in and basically try to make myself as thin as possible so I don't touch any part of the tunnel.
I also kept my eyes closed the whole time and just focused on nice deep slow breathing to avoid getting anxious.
I also found it comforting to hold my own hands on my stomach during the whole time. Then if I started getting stressed I could just dig a fingernail into my other hand and that helped distract me.
The time goes remarkably quickly though. I was in there about an hour and 15 minutes total, but I could've sworn it was about 20 minutes.
You'll be ok.
Starr