By default the Market entry card is 440px wide and the category sidebar is 175px. To change the overall width you need to change two Market enabled shortcode options. Here is an example:
[connections category_width=160 card_width=500]
You do not have to change both options, you can change only one or the other.
Here’s and example that makes the category sidebar wider:
And here is an example to make just the entry card wider: