Let me share a story about myself that may be relevant. I was a star in math in high school and was told I was great but had the same fears you express as to whether I could ever do anything really outstanding. I went to a good college as a merit scholar, was actually admitted over the phone and still thought I was the best thing since sliced bread. In college I did poorly but had all manner of excuses for myself. I bounced through more years without distinction, and kept getting free rides to grad school, and was told I was promising but never performed. Eventually they gave up on me and I had to leave school.
I spent years trying to recover some status, working hard, trying to learn some discipline and some hard math skills. Finally, maybe with the motivation of needing to feed my family, I made a discovery about myself. I had a fear of trying as hard as I could, in case I should find out I was not as great as pretended to be after all.
I realized I only had one last chance at becoming a mathematician. I had to take a chance, the chance that even if I gave it everything I had, I might still never be good. But that is the chance we all have to take in life. If we want to compete in the world, we have to give it our best shot, with no guarantee it will give us the results we hope for.
In my case, indeed I was nowhere near the great mathematician I had fantasized about. But I was miles better than I would have been without trying my best. If you want a guarantee you will succeed before you are wiling to try even the career you want most, you are handicapping yourself almost totally. One strategy is one I mentioned - give up credit for your successes and grant them all to those who helped and supported you, God, your parents, your teachers, your forebears, your students.
There must be other strategies as well. The point is to find a way to have the courage to give yourself a chance to succeed. Good luck. To quote the great Silvanus P. Thompson's "ancient simian proverb", "what one fool has done, another can". Just a joke, please take it as meant.