Very good. Let's be a bit more deliberate now.
1. Make sure you focus on where you aim those fireballs. Different areas of the body means different effects on your opponent.
2. Be specific on how many fireballs you release at your opponent. One fireball, compared to three, is a HUGE difference.
Lastly, in battle, there are three ranges that every jutsu has.
Short (0-5 meters), mid (5-15), and long (15-25+). These can affect how long your jutsu takes to hit your opponent and plays a huge part in timing of every battle.
Now, try again like you were actually fighting someone.