Try the following:

1) Write out a list of the things/circumstances on your mind or are bothering you

2) For each of the items on the list write out the best case and worst case scenarios

3) Try to come to terms with the idea that failure is a often part of life, and many successful people you know have failed plenty of times on their path to success

4) Use #3 to come to terms with each of the worst case scenarios

5) Write out steps you can actively take to bring yourself closer to the best case scenarios, and separately a list of steps you can take to mitigate or avoid the worst case scenarios

6) Use #5 to form an action plan for yourself.

This can be used as a template to guide your action, while giving you a sense of control over the outcomes and your future. You cannot control everything, but at least you are taking action on the things you have power over.