Set Maximum Width with Wexley Template

Site URL: https://lukebeebe.com/

On my 13" laptop the site looks good; But, on any computer screen larger, the 2 rows of 3 thumbnails become uneven. How can I set the max width on my website so that the main screen doesn't get larger than the 2 rows of 3 thumbnails? It only effects the home page and the navigation panel (which stretches to the margin of the screen you're viewing the website on). Thank you

Add to Home > Design > Custom CSS

.homepage div#canvasWrapper {
    max-width: 900px;
    margin: 0 auto;
}