The single-page form is great, however, for longer forms, it’s best to create multi-page forms. Divide your forms into sections and this way users will not be intimidated by endless forms.
Having a multipage form is recommended for longer forms so that your respondents could stay focused and fill it in. However, if you decide to remove the multiple pages, here is how you can do it.
In the Editor, if you hover over the space between two pages, you will notice that a button appears with Merge pages. Click on the button and voila! Your pages have been merged and now you have a one single page form.
If you combine them by mistake, add a new page break field in the same place.