Hey @hunginc, you're absolutely not alone with this! Overthinking can be so overwhelming, and you can often begin to question yourself on the smallest things, and that can come from a range of personal reasons, as you stated yours is the fear of failure.
Finding peace in your own mind is extremely difficult, and I think when we are surrounded by a never ending world of social media/screens/news etc, it is so normal to place so much uncertainty in our minds.
I wonder if you have tried or considered trying some kind of reflective practice e.g. journaling, or meditation/breath work?
This article also has some great tips on managing anxiety and stress, which could be helpful in giving some insight into how you might look to manage these constant thoughts?