Check your code in Dev tools to see if there is a class affecting the image. Since you have not posted the email code it's hard to say where/how it's breaking.
It might be easier to code a separate view online. Radio button functionality does not work on most email clients.
If you are sending emails from Outlook, it will strip media queries. Reason being when Outlook was around, media queries wasn't and is not supported on it.
Basically, what you see in Outlook is what will be sent
Just a quick note, Android 4.4 doesnt break columns into rows. You will need to use th's and use media queries to break it out. Support to break th into rows is on all email clients.
If you are using th, just add margin:0px;padding:0px; font-weight:normal; on your code and it will look the same across all email clients.
I am going with Charles on this. Another example I can give is, if your desktop design is 700px, you are resizing your hero image on iPhone 5 which has a screen size of 320px.
Technically you are viewing 2x image as its resized to be 320 pixels with original image being 700px. Let me know if this made sense.
Thats an old resource. Try this one from Google: https://developers.google.com/gmail/promotab/overview
You can test it right on the page to see how it looks