When previewing a site I created in Responsive Layout Maker on a large iMac monitor, my breakpoints work but only up to 1567 resolution width, which is as large as the Responsive Layout Maker goes. If I expand my window larger than that, the formating is lost. What am I missing?

Please help!!

Make sure to move the slider to the right of that breakpoint so that the white dot does not appear on the breakpoint. That is where you configure your layout higher that 1567.