When I apply certain filters in FCP, there will be a large white 'X' across the image in the canvas. How do I get rid of this? Or will it not be there when I export and print to tape?
What filters?
Do you see the image or just a thin x coverign the entire image? If that's the case it's showing a wireframe because it's not fast enough to display the image without rendering.
Check under View menu to see if it's set to wire frame display or make sure to do a render (option-R)