If I understand what you are asking correctly, it sounds like you should look at each of the keyframes before you want any rotation and make sure that each of them is explicitly set to 0 rotation. I assume each of keyframes 1, 2 and 3 are for scaling only. Then based on the rotation parameters in keyframe 4, your image will indeed start to scale just after keyframe 3. Sorry if I have misunderstood what you are trying to do.