It depends if the parabola opens upward or opens downward.
If the parabola opens upward, then (3,-3) is the lowest point and therefore y = -3 the smallest output possible. That would make the range y ≥ -3
OR
If the parabola opens downward, then the range would be y ≤ -3 since y = -3 is now the largest possible output and (3,-3) the highest point on this parabola.