Thank you for your post.
Checkbox fields in a browser take up a little more room vertically than FileMaker Pro. If you size the field to be narrower and taller, the checkbox and radio buttons will then display vertically in one column. If you place the bottom border of the field just below the last checkbox or radio button, it is very possible the last value (and maybe two or more) will be cropped. Therefore, drag the bottom field border quite a bit below the last value to allow Instant Web Publishing to display all values.
That did it, Thanks so much.