Have you read the guide about motion sensor placement and followed it to the letter? That's key before playing any game.
When playing golf on Wii, the power generally does depend on how far you "swing" the Wiimote back. My rule of thumb is to use the Wiimote as if it were an actual golf club and that gives me full power on any swing. By only swinging it a little way back, you limit the power alot and the results will be varied. Try using it like an actual golf club and see how it goes.