Teresa,
Wow good luck tomorrow. I can't believe that it was a week ago that I had mine done now! Wow does time fly. I was the same as you partly nervous and partly excited. I would say more excited though. Now learn from my mistake. make sure you ask what it is your seeing on the screen if they don't explain and if you see them measuring ask them what are they measuring etc. Ask to hear the heart beat and preferably longer than a millisecond which is all I got. Ask them to give you the photo's you want not just the ones they think you want. I wanted a pick of bumps bits so that I could see what it looked like so I could feel confident that they were right. If you get a DVD done ask them to record the entire session and not just 3 minutes. Ask them to record the baby as it moves on its own. Mine didn's stop moving and zooming in and out i just got dizzy from her jiggling around. I would have liked even 30 seconds of just recording the babies movements with out interuption. Um have I forgotten anything... Make sure you ask them to check again if you can't see what it is they said they are seeing and ask them to point it out until you get it. After all your paying them for the scan you might as well walk out of there with your expectations meet. I know its a medical scan but there is no reason why you can't understand what it is your seeing.

I look forward to hearing about your jelly bean!