go to: preferences/media/default media scaling and set it to Scale To Frame Size. all your pics and videos will be set to 100% when put on the timeline.
if you have a lot of clips that are set to “set to frame size” and they are too big or too small then select all of them in the timeline and right click and select “scale to frame size” and then you may have to go to each clip and in the motion tab hit re-set scale.