Flickr Gallery Number of Thumbs on page

Hi,
Great plugin!

I’m having trouble setting the number of thumbs on a page. I read the post about changing the gallery width but it didn’t work. On this page, you can see how the rows are not equal in number:
https://beta.johnnorwood.com/category/john-norwood-studio-images/
How can I fix this so each row has a set number of thumbs?

Thank you!