Confidence comes from character and competence.
If you lack character you’ll be worried about being found out.
If you lack competence, the same is true.
And if you’re worried about being found out, you won’t have confidence.
Competence itself comes primarily from good character: hard work, honesty (about where you’re at and what you need to learn and practice), kindness and gratitude towards others who can help you grow, etc.
So build your character first.
Be honest. Work hard. Express gratitude. Build daily habits. Stay humble.
It will take time, but your character will build your competence.
And the confidence will come.