Nrf24l01 sending multiple signals
You are witnessing button bouncing. You need to incorporate a "button debounce" in your code. What is happening is when you press the button your code continues to loop (e.g. cycle). The Arduino detects the button is pressed every cycle. If your arduino has a 16 mhz crystal oscillator its means 16 Million cycles per second. Thats fast, much faster than you press and release the button. 

There are number of why to solve this. One is using an interrupt instead of polling, but you will still need to incorporate a debounce. 

Google Arduino Button Debounce.