To embed a Custom Google My Map embed code into your blog post, please follow this video:
This is the code in the video that you need every time you will embed a map when publishing a blog post:
width="600" height="450" frameborder="0" allowfullscreen
Unfortunately, pasting the code straight from Google My Maps will not work and the only work around is to change the iframe parameters using the code above.
If you have further questions, please let us know!