Why do my effects outlast the clip they are on?

I am trying to do a simple highlighting effect using a couple of rectangles. It worked great, but unfortunately, the rectangles are outlasting the image they are mapped to by several seconds (see photo). I can't get rid of the extra seconds without getting rid of the rectangles entirely. Can you help out with this? I just want to adjust the duration of the effect, but can't figure out how to do it. 

Thank you,