You didn't do anything wrong, this is a cache issue which will most likely be fixed in Beta 8.
Do the following
Install Reflar/Uncache
OR
Run php flarum cache:clear
Run rm assets/rev-manifest.json
CHECK
If you are using Cloudflare, clear its cache
THEN
Hard refresh browser (CTRL+F5)
If that doesn't solve it, check another browser or clear your browser cache.