“Do not fear” isn’t quite right.  It’s kind of like saying, do not breathe. “No fear” doesn’t work either. That’s just false bravado.  It’s more like, “Do not fear the fear.” 

How not to hold back?  Realize that there’s nothing wrong with you, nothing wrong with fear or being fearful.  Lean in, explore and pay attention.  Spend time with it.  Become intimate with fear.

Do what scares you.  Risk everything.  Leap.

Smile at fear.