In most content management systems you will need to paste the Entry Form Embed Code (found on Step 5. Publish within the campaign builder) into an HTML editor (not the visual editor). This will ensure the code is saved properly.
Please note that in many content management systems, like Wordpress, the entry form may not appear within the 'Preview'. To view your entry form without publishing to your live website you can set the post to 'Private' and publish. You can then view the live content but your website visitors will not be able to.