The issue is with the difference in aspect ratio of the image in the left and right columns. In the screenshot below, you will want to assign a background color to your column. See https://youtu.be/ZKrU4wWcrrU
This grid setup is best achieved using either The Grid or Essential Grid plugins though. Please check out the demos below.
For more details about those plugins, please see the links below:
If you wish to continue with your setup, seeing this setup demo might help.