As shoulder, waist and arm turns to the left, the ball travels smoothly as intended to the other side of table and will not go outside.

If the turning of shoulder, waist and right arm is not ample enough, the ball would travel flat and land offside. With this knowledge in mind, to avoid ball going outside, players not used to the turning of body often have to keep the ball down using forearm which subsequently lifts the elbow. Likewise, to lead the ball to land on opponent's side, they also have to push the bat somehow downwards at the price of raising elbow. Amazingly, some learner players even use elbow to help the turning of body. This habit normally carries through to higher levels. Players have to bear in mind that they cannot solely rely on bat and arm to lead the ball. The cure is repeated basic training of long shots. The practice of long shots will gradually correct the mis-use of elbow. If, however, the problem remains, try to halt the follow-through arm at about 30cm after ball contact and let the shoulder-waist-freehand lead it to carry on turning. Hopefully it will help solve the problem.