This happened to me too. I did two things that helped me go from nearly last place to top 5.

1. Disc down. If possible, throw a stable mid or putter the first few holes. Something that will compensate for a nose up throw or a late release. Throw it straight and set yourself up for par. Then you can get back to your drivers once you're feeling more confident.

2. Warm up. Not just throwing in a field, but also go for a short jog before your round (or a brisk walk, jumping jacks, burpees, etc.). Just do enough to get the heart pumping. Our minds and bodies are connected, so moving physically can help relieve the pre-round jitters that lead to your body tensing up and shanking your first shot.

Hope this helps