What you are describing is performance anxiety, which is something we all experience to some extent. Congratulations to you for being able to cheerlead despite feeling so nervous. The good news about performance anxiety is that there are things you can do to help yourself.
We all have arousal and stress reactions, which are essential for human survival; they enable people to pursue important goals and to respond appropriately to danger. In a healthy individual, the stress response ("fight, fright, or flight") is provoked by a genuine threat or challenge and is used as a spur for appropriate action. Anxiety, however, is excessive or inappropriate arousal characterized by feelings of apprehension, uncertainty, and fear. The word is derived from the Latin, angere, which means to choke or strangle. (think about it - you think you are going to "screw up" or choke). It is often not attributable to a real or appropriate threat and can paralyze the individual into inaction or withdrawal. Anxiety can also be a symptom of other psychological or medical problems, such as depression, substance abuse, or thyroid disease.
Physical symptoms of anxiety include a rise in blood pressure, a fast heart rate, rapid breathing, and an increase in muscle tension; intestinal blood flow decreases, sometimes resulting in nausea or diarrhea. The psychological components include overwhelming and irrational fears that can vary in severity. People can avoid or at least endure these situations, but in some cases, the anxiety associated with the feared object or situation can be incapacitating.
Performance anxiety, or stage fright, is a subset of social phobia that occurs when a person must perform in public; symptoms include pounding heart, dry mouth, and tremor.
If you have a true anxiety disorders then treatment is required. Most anxiety disorders respond well to treatment. At present, the most effective approach for most anxiety disorders is a combination of cognitive-behavior therapy (CBT) and medication.
A healthy lifestyle that includes exercise, adequate rest, and good nutrition can help to reduce the impact of anxiety attacks. Rhythmic aerobic and yoga exercise programs lasting for more than 15 weeks have been found to help reduce anxiety. Strength, or resistance training does not seem to help anxiety.
Talk with your parents and/or doctor about how you have been feeling. An evaluation by a psychiatrist (a doctor who specializes in treating anxiety) might be a good idea. They can talk with you and help you decide if treatment is the right idea for you.