Form with table has text input fields that are too small and stay too small after data entry

Please try injecting this CSS code to your form in order to increase the fields width: 

td.form-matrix-values input {

    width: 100%;

}

This guide will help you injecting the code to your form: https://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes 

I hope this helps.