You can’t really “force” a line to contain 60 characters, like you might do with a word processor or your terminal window; that’s not how HTML/CSS is designed to work. One option would be to use some custom CSS to remove the text wrapping on the <pre>
tag. Your readers would have to scroll horizontally to see the entire text, but that might be preferable given what you appear to be doing.
pre {
white-space: pre;
word-wrap: normal;
}
Don’t edit the theme files directly, otherwise your changes will be overwritten whenever the theme is updated.
An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS.
As alternatives, you could either install a standalone custom CSS plugin, or create a child theme.