Start from a design, not from nothing
The slow part of any invitation is the empty page: deciding where the names go, how big the date should read, what order the details come in. A template skips all of that. You choose from dozens of finished, mobile-first designs and then do the only work that matters, which is editing the words that describe your shower.
Think of it as six lines rather than six layouts. Once each line says something true about your day, the template is done. The design, the spacing and the phone readability were handled when you picked it, so you spend your effort on content, not on arranging boxes.