Stop worrying about being sure you will win or do a great job. Start doing and maybe the great job will happen.
How many opportunities do we all leave on the table because we don’t have the confidence and we convince ourselves that we can’t do it?
Too many.
Only the narrow-minded fool will hate you for paste mistakes when your present successes far and away trump them. Don’t worry about the mistakes as long as it’s not your final project. (never stop working!)
When you start even if you don’t have your precious confidence, that attitude that drives you to start will drive you to start again if you fail. Apply what you learned in that failure and keep going.
Also, don’t worry about whether you win or lose. We all win some and lose some, but we absolutely control the effort we put in and how we recover from the setbacks. Get going.