First of all, I set up a Freenom domain (free domain, if you want to know). I used CloudFlare to set up the CNAME records, and the target was the custom domain Repl.it allows you to set.
But then, a plot twist happened: It wasn't reading the record. I've set it up perfectly with no errors. My disappointment is immeasurable and my day is ruined.
Freenom sometimes does the big dumb and doesn't work. Try creating a www subdomain and see if that works. If it doesn't, wait 10ish hours and try again.