In-game Improvement

Hi I wanted to know what the best way to improve my in game handling skills would be. I have amazing ball handling skills outside of the games but in game i always loose my dribble or the defender steals it. However, i am really good at all the dribbling drills my high school coach makes us do. What should i do to improve?

You need to play lots of 1v1, full court 1v1, maybe 2v2, and other game based drills that help you learn how to handle the ball with defenders in your face and in game like situations. See some of the game based drills on this page:

https://www.breakthroughbasketball.com/drills/dribbling-drills.html

Also make sure you know the fundamentals of protecting the ball, using retreat dribble, changing your speeds, dribble with eyes up, etc. If you need help with those fundamentals, this app can help:
https://www.breakthroughbasketball.com/pr/bhworkouts.html

Just play a lot of games with your friends. Maybe fear/doubt is what is impacting you because a real game situation and playing with friends have different mood on a person. Just always take advantages of space you have and attack on a right time.