There is a communication issue here.
What exactly do you mean by "make 3 shots" ?
Do you mean you want the player to be limited to 3 attempts at shooting or do you mean for the player to shoot 3 projectiles at the same time ?
As you stated this is the basic code from the example.
That example does not contain any limitations about the number of shots the player can take.
If you want to limit to 3 total shots, then simply add this limit yourself.
Add a global variable "ShotsFired".
In event "On touch end" Add 1 to ShotsFired.
In Event "isAiming = 1" add a condition to check that ShotsFired is less than 3.
This will limit your player shooting more than 3 times.
This is because of how events work.
The event sheet is read from top to bottom, the conditions for each event are checked, and if they are true the actions are executed.
If any condition of the event is false the actions are not executed and the sub events for this event are ignored as well.