Blog Posts in two locations

I am trying to put blog posts in two categories show they show up in two different places, but it’s not working.

On my home page, for the Blog Slider, blogs categorized as “Blog Posts” show up. On my right sidebar widget, blogs categorized as “uncategorized” show up. I want some of the posts to show up in both places, but even when I click both boxes to make the posts “Blog Posts” and “uncategorized,” they won’t show up in both places.

Is there something I’m missing? (I’m very inexperienced)