Meet warm-ups can be intimidating for any swimmer.
Try the following tips to make the most of your warm-up time:  

1. Check out the pool.  Notice the lines down the middle of the lanes (so you won't circle swim), the Ts at the ends of the lanes (so you will know when to turn), the flags (for your backstroke count), and the blocks.
2.  Leave space.  If possible, leave 5 seconds between you and the swimmer in front of you.  Keep your head in the correct position, looking down instead of forward.  
3.  Warm up with perfect technique.  Streamline with powerful fly kicks, work on distance per stroke, and get a great feel for the water.  
4.  Get your heart rate up.  Going fast during warm up will not use all your energy.  Listen to the directions your coaches give and try to implement everything they tell you.  
5.  Know your backstroke count.  If you are not sure, swim with your regular count and kick in to the wall on your side until your touch the wall. 

Take 3 deep breaths and have a great time at your next meet!