I think you can pull your right elbow back more while delivering the ball to generate speed. Record yourself bowling for few minutes and preferably not in slow motion lol. Make sure most of them are your stock ball. That looks like the delivery that goes into the righty. I think you can put more revs on the ball, try using your fingers and wrist more they generate more revs giving you more drift and dip.
When you are delivering the ball, an off-spinner should hold the ball with their index and middle finger on either side of the seam, the grip you were using is ideal for a skidder/slider by flicking the wrist. This imparts less spin on the ball, but maintains slight deviation. Good for getting outside-edge.