If you inspect the widget’s output with your browser’s development tools you should see an encasing DIV that has a class of widget_custom_menu_wizard. It’s quite likely that the DIV will have one, or more, other class(es) as well, such as widget_wrapper. It’s also quite likely that your theme will already have applied some styling to the DIV.
You can add your own css rules, or change what’s already there, to create the amount of space that you need, using either padding or margin.
An example might be something along the lines of…
.widget_custom_menu_wizard {margin-top:2em; margin-bottom:2em;}
If you are using a child theme, you should be able to add your css rules to that child theme’s style.css file. If you are not, and you do not wish to consider doing so, then you will need to modify your theme’s style.css … but be aware that any changes you make will be lost when/if you update the theme!
