It's a nice idea for a game, as most of those tossing games are sort of one clicking to target the angle all that while this one allows one to choose the angle and speed.
I do believe that it's better for you to create a main menu and instructions menu. As I was abit confused in the beginning. I would also suggest you to make the targetted plant further away and add in a scroll so that players can scroll about through the game. It's abit confusing but what I mean is that the plant is out of the screen so players have to scroll to the left or right until they find the plant and the distance. Also it would also be good if a zooming button is accompanied with the scrolling thing.
Also, animate the sheep a little bit, like when it is going to hit the red plant, it will scream and splat when landed on the red plant.