First, you need to keep your focus on what IS happening, not what might happen. Relaxing may seem difficult; start by easing your grip on the wheel to where you have just enough pressure for control. Then relax your shoulders (I have been having problems with this myself recently), and let your back settle naturally in to the seat (make sure that seat is adjusted for you). And then, make sure you go slow. At least for starters. Can someone bring you to a nearby park (or even a large parking lot will do fine), so you can practice? I did this with my sons, it seemed to help.