A lot of cheerleading motions do not feel natural until you've been doing them for a while. Often, motion positions can feel correct, but aren't. When hitting any motion, you want there to be a straight line from the middle of the knuckle on the back of your hand to your shoulder (or elbow depending on whether or not the motion half or fully extended).
The best way to train your arms is to practice in front of a mirror (or large glass doors and window at your school or gym). This way you can see the difference as it happens and eventually what is actually the correct position will also feel like the correct position and become a more natural movement.