Matching drag and drop

Unfortunately, you can't control the size of the boxes in a default Matching drag-and-drop question. 

You can, however, create a Freeform drag-and-drop, which would allow you to make the boxes any size you want. 

Here's more info about Freeform interactions: 

https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-convert-existing-slide-to-freeform-interaction