We all face uncertainty in our lives.

Some of it is welcome and some of it is not. We all enjoy a nice surprise, but not knowing how to deal with a specific situation or what will happen next is very uncomfortable.
The way I deal with this uncertainty is relying on previous experiences. The first time I ever massaged a client in my Roseville office was a very scary experience. Massage became a comfortable activity after lots of practice. I can see that transition in myself and use it as I face upcoming uncertainty in my life.
Try to use this approach with the variety in your life. I know starting a new workout program, working out in a new environment, or competing in an important race are all scary activities. But I am sure you have had successes similar to the challenges you are facing today. Have you ever started a new workout program in the past? Entered a new environment? Competed in a race you cared about? Remember those experiences and how comfortable they are now. Rely on those memories for confidence as you face your current situation.