How old is the guy you will be fighting? How big is he? Any knowledge of his muay thai credentials?
While it may be frightening at times, I think its best to know what you are up against. In the finals at the NAGA tourney I entered I knew a bit about the guy and he was older, bigger, and he had more time in judo than I had in wrestling and bjj combined. That being said I knew what I had to do to win, and I was a coward but I beat him on points. All that said sometimes you can't know anything about the other guy and that makes me more nervous.
I'd say if you trust your trainer and he thinks you are ready then you are ready. Its scary, frightening and I pissed 8-9 times in the hour before my first amateur kickboxing match. My dick was so tingly and uncomfortable from all the nervous pisses it was.. not good. But there is a point that is went away for me, I gained more confidence in myself and I relaxed. Getting through it, getting past that anxiety and measuring myself in a way that only a fight can do is the greatest feeling. As bad and as scared as you will be before the fight is how good you will feel after/during.
It is your call, I think you should do it, if you don't no worries but remember courage is the resistance of fear, the mastery of fear, not absence of fear. Mark Twain said that.
check your rep