Crop Video to Frame

Do you mean you scaled up the view magnification so that portions are outside the Comp window preview, and you want the actual composition frame to match that?

Or do you mean you actually used the Scale and Position properties on your video to get it to center and fit within the composition frame?

Normally you would achieve this using the second paragraph above, because any content outside the comp frame will not be included when your final video is rendered. In  other words, if you do it the right way, you don’t have to crop anything. If what you did was the first paragraph above, then what you want to do is get it done using the Scale and Position properties as in the second paragraph.

Not sure that you need to do this but you can select the video in the timeline then use the rectangle tool to draw a mask the same size as what you're viewing in your comp window.