Hi! I used to have the same problem as you, and I would get so frustrated because I knew I could do so much better than what I performed at the meets. I have some tips that have helped me:
1- First, keep a positive mindset. Don't say negative phrases in your head like "I hope I don't fall" "Don't wobble" "Don't take a step" "What if this happens" etc. Instead replace those thoughts with something more like this "Stay tight" "Keep calm" "Point your toes". Basically tell yourself what to do, not what not to do, if that makes sense
2-Don't put extra pressure on yourself. Know that mistakes are bound to happen (nervous or not) and just laugh it off and focus on what you can do better next time. It is all a learning expierience. It is not the end of the world to have an off-day, so it is important to be able to shrug it off and focus on next time. Always remember failure is part of success!
3- When your at practice, put yourself in a pressure situation. For example have your team watch your routine and pretend it is a competition. Or play a game with your teamate where you do your routines and compete against each other with some sort of point system.
4- Trust your training! Know that you probably done these routines hundreds if not more times. It is just another routine.
5- Have fun! Cheer on your teamates and create a positvie atmosphere, this will help keep it fun. And the most important thing is you are enjoying it, and when you are having fun you are more likely to do your best