Practice. "Fear lean" is really common. it's your mind's reaction to sliding downhill. It wants you upright which, against the slope of the hill, leans you backwards. You have to train this behavior out of your brain.
Here are some things that might help, leaning backwards is going to make you go FASTER it's also going to eliminate your ability to initiate responsive turns. When you start feeling the fear lean, stop. Take a second, and then continue downhill.
Keep riding and stay in control. This behavior will correct itself over time if you do.
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