The size and aspect ratio of the component can be customized in Widget theme - Advanced Settings. Regardless of the actual size of the videos assigned to the component, this is going to determine how the component is going to appear on your site.

For carousels, you can go to Edit -> Advanced Settings -> Layout -> Change to 1 (this will make the video appear bigger).

For Single Video widgets, you can go to Edit -> Video Thumbnails -> Thumbnail format and change to a fixed size; this way you can adjust the size of the widget any way you need.

This option is only available for embedded widgets.