Do your absolute best in practices. Show your coach that you work hard and that even if you are not good enough yet, you have it in you.

Try to instead of panicking when getting the ball, protect the ball instead. Use your pivot foot and dribble if you have to.

Try to protect the ball when driving. Practice different pick ups ;)

Simply play a lot of basketball, and do your best at practices. As long as you push yourself hard every day your stamina will improve

I would look at other undersized guards and analize what they do. Look at kyire for an example: he uses hus size to his own advantage. He learnt how to be quicker than everybody else, how to dribble, and how to finish at the basket without getting blocked. Hope this helped you a bit!