How can I make the input column wider?

I the input table to be larger

You can increase the Table and Column width, inside of the Field Properties. 

And add this CSS code to the form:

.form-matrix-table {

  max-width: initial;

}

How to Inject Custom CSS Codes

Here is a demo form - https://form.jotform.com/93015558199971

Feel free to test it and clone it.