Do you have an injured shoulder?
As you've already noted, you need to keep your elbow of your hitting arm from collapsing against the body. Just keep it up and out. Also, I wouldn't advise pausing in your racket drop position.
Time your pause at the trophy position, don't move from trophy to racket drop, pause, and then swing up at the ball. Keeping your elbow high, pause at the trophy position and then let the hand lag as your shoulders turn up toward the ball and your elbow moves toward the ball. It should look more like throwing. And the movement from trophy to contact should be continuous.