This is because with the Free-Form editor you are using raw HTML to construct the email. To achieve true 'responsive' design - i.e. the content resizes to the dimensions of the device it is being displayed on - requires extensive HTML skill and knowledge to implement.
Starting the draft again and using one of our plain email templates rather than the Free Form editor is better at guaranteeing good results across devices and resolutions.
When you go to 'Pick a Template', you can choose Plain Emails from the drop down menu to view the plain emails, then copy the text into the relevant boxes and replace the images with the ones from your draft. Your email will then display correctly.