I no longer compete in Judo, but I remember my first tournament.
The night before I couldn't sleep so I got up at 2am and had some leftover pizza. The next day I had an awful case of diarrhea. The three hour trip to the tournament was brutal. As soon as we got there I was ready to visit the bathroom, but we were running a little close on time so everybody hustled to get registered. We were directed to immediately weigh in. The weigh in was in a locker room so luckily there were toilets there.
Unfortunately, the stalls didn't have doors, and the scales were directly in front of the toilets. Well, sometimes you just gotta go, so I got permission from the weigh in guys to go poop. One other guy was trying to loose a pound on the toilet so he could get in a lighter weight class. At least I wasn't alone. Everyone was trying to be discrete and not look in that direction, but it was an uncomfortable experience for all involved.
My first Judo tourney started with quite a bit of embarrassment, but I won 2nd in my div. I think I had a psychological edge on my opponents, though. They probably thought I was crazy.
Just remember to be respectful to the officials, your opponent, and your art. That is one thing that always sticks out to me at tournaments. If someone wins or loses a match and proceeds to act like a fool it will be noticed, and remembered. If you conduct yourself with dignity - that too will be noticed and remembered, regardless of the outcome of the match.
Good luck. Have fun.