Recent Posts image/txt position not lining up properly

This CSS may do it:

.thumbnail img {
   margin: 0 auto;
}

To add CSS: If you are using WordPress 4.7, use the “Custom CSS” option in the customizer. If your theme has a custom CSS option, use that to add the CSS shown above. If not, install the plugin Simple Custom CSS. Or, if you have Jetpack installed, enable its Custom CSS module.

Learn the Chrome Developer Tools to help you see and test changes to your CSS.