Being nervous is a normal passage to go through prior to competeing! I always believed and taught to prepare yourself void of excusses so that you can take your nervousness and turn it into positive energy! You need to learn to relax so you don't leave your energy in the locker room but knowing that your preparation was done successfully and your ready willing and able to compete gives you the convidence you need.
I practice this approach using my spar sessions as if they were fight time so that I have a formular to use! It worked well for me until I got some experience under my belt!
Get you body right, then your mind has no doubts! Ray.