You should not capture whole page, that will make screenshot image too blurred. I think you can screenshot whole page, then crop to use only part of your extension display, or a bit more around list of merit senders in OP. The image will look better.
Furthermore, you can use following option to adjust your screenshot.
People who don't install your extension, will don't know how it looks like, and they won't give your merits for your works. What a pity when you do great works, but are not recognized because bad-quality screenshot.