I can't stop doubting myself

Doubt your doubts!

When you catch yourself doubting, take a deep breath and say "It's ok". Doubting yourself can become a habit, once you break the habit you can move on.

Welcome to the world brother.
Much of life seems designed to get you to do just that !

Doubt that you can continue doubting forever.

Yeah you can. Have faith.

Write down your doubts on a piece of paper and then when you're done, throw it in a bin.

Sooner or later you are forced to exceed your expectations of yourself, after crushing one doubt hopefully they'll all disappear.

No one is perfect.
Go into everything anticipating your going to probably screw up, dont do it intentionally, but always keep the thought in your head. "No one is perfect and they are not gettin perfect outta you."