Scratch

I'm making a game I think is fairly basic. Except for what I'm asking. I'm making a game where you are just crosshairs and you have a green blob as a bullet.(Your trying to kill the space ship moving down the screen.) I've made it easy for when you click, the blob keeps getting smaller, then eventually comes back to you. But, my question is, what should I do if I want it to be able to shoot multiple times? If you need the code I'm using, I'd be glad to give it. Thanks to anyone who tries to help!