It looks like you have a good start going, a well placed fastball is baseballs best pitch, changing speeds on that, keeps folks off balance and being able to hit your spots means you have command of the zone, now as for your breaking pitch, you have to develop it, you will not have much luck if we tell you to "flick" your wrist and you attempt to throw it on Tuesday.
Not that we would just tell you to flick your wrist.
The slider is a dangerous pitch, like any, if it is thrown right it is not going to cause damage, but most kids want to spin that sucker, leading the ball with the pinky finger they roll their hand under the ball (Ouch!). The slide piece is a variation of the fastball believe it or not, so your fingers HAVE to be behind the ball.
Have you asked your coach about it?