How to make all label fields full width

You first need to go the SCRIPT section and add isLabel() function:

function isLabel(field) {
  return CONTAINS(DATANAMES('Label'), field);

Then, you will need to use this function in the BODY section just before the last <% } else { %>:

<% } else if (isLabel(element.dataName)) { %>
      <div class='field'>
        <b><%= element.label %></b>

How to make the text of a specific label field appear bold

Within the element.isLabelElement if statement, you can add conditional logic to bold the text of the label:

    <% } else if (element.isLabelElement) { %>
      <% var fontWeight = "normal"; %>
      <% if(element.label==="your_label_dataname") fontWeight = "bold" %>
      <div class='field'>
        <h2 class='field-label-full' style="font-weight:<%=fontWeight%>;"><%= element.label %></h2>
    <% } else { %>