The aiming is from the center of the screen so that might just be the shotgun throwing you off. There's patch coming out fixing the ceiling collision which would make the ball fly off course.
It's not left click, it's hold and release. The zoom in effect indicates the power. Watching your video it seemed like you had less than optimal fps. Try lowering the settings to at least get a stable 30fps.
The holding button to remove tutorial text is there so people don't accidentally click it away, it's pretty standard to do with tutorial UI.