1. What you see in the preview window of the video editor is not the size of the output video, but the actual size of the output video (the frame size set according to the project). As the video becomes smaller during the project playback, you need to reset the frame size in "Project Settings" (except the original video itself is small, otherwise the output video will be blurred);
2. Of course, if it is not saved in the video format set in the project (that is, AVI or MPEG), when outputting the saved video, you can set the frame size to be the same as the original video in the options.
The method of material deformation in the recommended answer is not desirable, and the image is distorted, so what is the value?