Honestly, I didn't think I-day was that bad.
I had said my goodbyes the day before, had a good dinner, etc.
Most of I-day is standing in line. If you don't let cadre yelling get to you, it is not that bad.
Yes, you will be nervous (I was too). Don't worry about it too much. Basics' brains turn to mush for the first couple days. They all want to do things right, but they have no idea what "right" is. It took me a 5 minute speech to get them to take out a bar-coded sticker and place it on the tag of their duffel bag!
(You never know how hard it is to give directions, until you realize you cannot assume the other person will do anything logically, lol.)
Now, day 2 sucked!