What can i do to not be so nervous at a horse show?

On sunday im doing a horse show and it is kinda my first show and my first time riding this horse in a show and my first time off property, but hes been there many times. Last year i did a home show on one of the horses and i was so nervous and he was too and he just freaked out and took off and wouldn't stop. This year im more experienced. ive jumped 2'3 of this horse and would probably trust him with my life!! i love him so much and i believe we can do good!! Last night in my private lesson we did amazing and it was my best ride ever. perfect jumping, i had good equitation, he got the right leads, nice slow relaxed canter. but tonight some friends and i that are all showing sunday got together and had an instructor treat it like it was a real show. im friends with the instructor and friends with the other 4 girls but i was a mess!! i was just so nervous and he felt it! hes a pretty slow quarter horse but he was basically racing around the ring and taking the cross-rails so big and long, which he never does!! i was also super stiff because i was so nervous!! i think that is stupid because i was free riding at my barn with my friends and i was so nervous. sunday i am going to an off property schooling show. its a schooling show so its not a big deal and im doing beginner equitation which is WTC and 18inch cross-rails. im so excited but anxious for sunday!! what is some stuff i can do to just chill out? like i know how to ride this horse and we do really good together i just got like so nervous today, and that wasn't even the show!! please help me!!