I’m not familiar with amazon-adsystem so the first part of this suggestion will be me just spitballing.
My guess is that the add doesn’t have padding or margin but rather is aligned to the right and has a specific width.
I know that google adsense allows you to limit ads being displayed to specific dimensions or to be “responsive”. You may look and see if this is an option with amazon. If so then you could define ads that will take up the extra space.
Alternatively, you can place the add inside a container like Joe Workman’s CSS box or Big White Duck’s Section Pro and then apply the appropriate amount of padding on the right to offset the alignment and bring it to center.
Thanks Brandon and I appreciate it! You are right that adsense ads seem to align to the right side of the stack and I want it either to center or allign to the left using the 2-column responsive stack. So, I have been customizing the ads to custom width, however they still do not align with the text in the html stacks with the text stacks.
So I guess I will have to look at Joe’s CSS box!