your html file contains the following CSS:
The "-15px" is pushing the leftmost 15 pixels, i.e. the first column of checkboxes, out of view.
If you remove the "margin-left: -15px;", or change it to a positive number, you will be able to see the leftmost checkboxes.
By the way, the html file is also missing the the markers which tell the HotPot module where to insert the submission form. Therefore, I recommend you add the following two lines just before the </body> tag, which is located near the end of the file.
<!-- BeginSubmissionForm -->
<!-- EndSubmissionForm -->