Mask Shape Matte Video Filter Help Needed for Final Cut

I am trying to add a Mask Shape Matte Video Filter to my video but when I add it, the Mask Shape does not appear in my Viewer Box. Not sure what I did, but now it appears, but when I change the scale settings, the filter does not automatically update on the Canvas. Why is this happening? and what settings do I need to change to have the Canvas update in realtime? I am sure there is a simple answer. Thanks.