You indicated that the angle between the velocity and acceleration at point D is obtuse but not 180°. An obtuse angle smaller than 180° indicates that the ball is slowing down while following a curved path. Is the ball slowing down 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?