Hi Mary,
The only available control for adjusting the width is named ‘columns’
When you enter a value for ‘columns’, you are choosing how many 11ths (elevenths). Let’s say you enter ‘2’. That means your field will take up 2/11 of the total width of the grid/list. (Please note there are various exceptions, but this is the general idea.)
There are no easy workarounds. The difficult workarounds involve writing your own HTML and JS to create custom layouts and grid designs. You can read more on this topic here.