The push shot is so close to the ideal shot. It's normally struck well on a good trajectory and just ends up right of the target you are aiming for.
It just boils down to one simple thing: the clubface is slightly open as it strikes the ball.
To prevent this happening you must learn to co-ordinate the body and the clubface to arrive at the ball together. If you can do that the clubface will be square when it strikes the ball.
Watch this video instruction tip to learn to co-ordinate your arm and body movement so that you can avoid the push shot out to the right.