Stay calm. Have a solid meal so you have good energy. Also make a personal playlist of music so you can tune out distractions and get in the right mindset pregame. Finally, just play. After the first bucket or two you will settle down and realize its just another game. Good luck.
Work on the stuff your having trouble in, like if u can only make 4/10 jump shots, practice before the game starts and try to make 5 or 6/10 CONSISTENTLY. Being a player myself that's what I did and being a center and hitting from middle range fells great! And it builds confidents! Good luck.