You indicated that the acceleration at point D is opposite in direction to the velocity. When the angle between the velocity and acceleration is 180°, then the ball slows down while moving in a straight line. Is the ball moving in a straight line at point D?

In addition, remember that at point D the ball is flying through a vacuum. Hence, the acceleration of the ball at point D is the freefall acceleration (i.e., the acceleration of gravity). In what direction is the freefall acceleration?