Well, it depends what "speeding up" means. Usually in problems like this they ask you to show where the veliocity is increasing and where it is decreasing. If that's what they want, then you have it correct - velocity increases if the slope of the velocity graph is positive. However, if they really use the terms "speeding up" and "slowing down" in the question then we have a problem, as in general usage "speed" is a scalar, not a vector. Consequently "speeding up" means that the absolute value of velocity is increasing, and "slowing down" means the absolute value of the velocity is decreasing. Here from t = 2 to t = 3 as the velocity becomes more negative that would be thought of as speeeding up in the negative direction. So - please confirm the wording of the question, and tell us whether that changes your answer or not.