It's all about technique, the best way i can explain it is like this:

You know when you tense up your head so hard that it shakes or vibrates. Well try doing that with your arm.
My finger is kinda vibrating over the button rather than pressing it, its a technique i used as a kid on oldschool shooting games lol.

Btw i saw your score uploaded on the site, nice one. You were only 1 press away from exploding the melon