You would do well in showing us your styles.css file too. In case you haven’t used it at all, then worry about the structure of your page first and once you get that done, start with its design. The display of images falls under the design category, for which CSS is necessary. HTML only structures the page.
Just to make sure, is it currently showing as one column only? That might be because you gave them a width of 100%, though to be honest I’m not sure. Maybe try 50%.
Have you tried using flexbox? I haven’t gotten as far as the Build a Personal Portfolio Webpage course, so I don’t know if you’ve been shown an alternative, but maybe flexbox is what you need.