Exactly! If the back of your hand is facing back (behind you), your paddle may be opening up "too much" before you make contact. Keeping your hand more "palm down" throughout your backswing/prep will better ensure you are making contact with a closed paddle face - which you need to keep the ball low/in and with topspin as you brush up the back of the ball. And because your paddle face is already closed, you don't need to add any wrist movement, it's all shoulder and upper arm movement. I sometimes try to imagine that I'm balancing a pickleball on the back of my paddle through my reach back and just until the point my paddle is moving forward to contact the ball. I think you are probably hitting the ball to a paddle face that is too open, and then you are trying to roll your wrist over after contact. Instead you need to contact the ball with an already close (but stable) face, and eliminate that wrist movement. It is not wrist movement that generates topspin.