The problem is that SharePoint has a lot of styles loaded in CSS files to control the layout of these field, and when you send the HTML in an email you don’t have (and cannot have) those files included.
There isn’t much you can do about that unless you use code to modify the HTML code adding inline styles to for example the <p> tags, but this is more or less impossible if you want to ensure it renders exactly the same as inside your SP form.
Alexander