There should be a different button to throw, rather than pressing space twice. More than once, the mechanic didn't work when I did it, or would only throw after I changed direction, making it pretty useless.
The hit detection takes a bit to get used to, because it doesn't feel like there's any depth on the screen. It doesn't seem like it's the shadow that matters, and any pixel, no matter now slightly it brushes the line, can trigger it.