Richard Arbus

I have croped a video and am trying to export it to upload it to youtube. I am trying to get the right image size. But the video is not filling the screen. There is a big black frame around the video although I chose to resize the video when iwas asked just Before the export . Pleas see the video on youtube: you see the film is small in the middle. How shall I make tthe film bigger ? I have chosen different fps (720 and 1080 in youtube format ) in the export menu. Thanks a lot for your help.