How to remove whitespace around the photo after cutting a portion of the photo in Photoshop?

I rounded the corners of a photo using an approach that involves me cutting a section of the image. The Photoshop canvas was showing through. Now, my image has white edges. How can I fix this.
The video I watched to round the corners is less than two minutes. Here is a link.

I have also attached a copy of the image.

See original post by wheelstb