Columns Gap Feature Not Working

I’m trying to set up 3 testimonial boxes in a row and I want a gap between each. The “Column Gap” feature isn’t working and when I try to do it manually (setting a gap by adding to the margins of each column) it puts the third column below the first one.

This is the website (but it might be changed by the time you see it): https://www.theapcoach.com/testimonials

Thank you for your time!
–Morgan