Try deep breathing.
When we are feeling anxious, our breath may quicken and also become shallower. When you notice your anxiety, or as you work to keep your anxiety at bay, take 2 to 3 deep breaths, inhaling and exhaling so your abdomen expands and contracts. Deep breathing like this can trigger the body's relaxation response, which can reduce your feelings of anxiety and help you to regain focus.
Consciously relax.
Try to relax muscles in your shoulders, arms, neck, legs, etc., or to alternate tensing and relaxing your muscles. By relaxing your body, you may be able to also relax your mind and approach the test with more calm and comfort.