Tried to resolve redirect issue, now all urls -> 404s

I use a popular cache plugin, WP Super Cache (note– this is not a plugin specific problem, I believe, hence me posting this here) and was trying to fix a redirect issue. Visits to domain.com didn’t redirect to https://www.domain.com, and all visits were showing a cached page from about a month ago.

In fixing this, I was suggested I add an htaccess file to my domain directory, because for some reason there wasn’t one there already. So I did so, and this was its contents:

RewriteEngine on
RewriteCond %{HTTP_HOST} ^domain\.com$ [NC]
RewriteRule ^(.*)$ https://www.domain.com/$1 [R=301,L]

The result? All domain.com visits redirected to https://www.domain.com. But now, EVERY OTHER URL on my site is a 404. And it’s not a 404 generated by wordpress and styled by my theme, it’s just a generic browser-based 404.

I’m pretty screwed here, and my site gets a solid amount of traffic. Any advice would be huge!