Not quite sure what you mean.
It looks perfectly fine to me.
Adjust the mask x and y to position the centre of the mask, and use the height and width to adjust the size. You may want slightly different values than Kent uses in the course, depending o the position and direction of the light source in the scene.
If you are thinking that the blur looks like a low resolution image, don’t worry, it’s not an image, the intention is to blur the mask so you have a gradient of light to dark, then with the overlay node, darken the rendered image furthest from the light source.
Don’t forget! Your render is only at 50% resolution too. When you’re done and ready to render a final image, crack it up to 100%.
