How to manage anxiety just before flying?
It is normal to have anxiety when experiencing something new.  These "butterflies" of the stomach are your body's reaction to your minds confusion over a new situation.

This is where training and mental discipline are key.  Rationalize what is making you uncomfortable and focus on your task.

Looking down at my landing gear while flying along at 2000 feet somehow made me more nervous, so I learned to focus on the horizon and to calm down.

Put what is bothering you aside as best you can.  With experience, your mind will differentiate and sort out what should be making you nervous (losing a wing), from what should not.  Then your body will not react (by being nervous) to normal aspects of flying (departing, cruising, landing).  Enjoy the view!