We no longer have ability to publish a trial site on Business Catalyst unless you are left with a any free or paid sites.
However, you can still manage your existing sites. In case you are unable to do so, there might be a possibility that your trial site has been expired after the recent Business Catalyst update - Why did Adobe take down my Business Catalyst website.
If above is your case please reach out to the BC support through the normal BC support page: Adobe Business Catalyst - Contact
Or through the BC help and support center: Business Catalyst Support and get your site enabled
It might take a bit longer than usual due to a higher load on the team right now, but the Support Team will gladly help you.
Can’t I host my site somewhere else? And then view it on all devices?
Yes you can obviously host it anywhere who supports FTP/SFTP, but then check with your host to if they can keep your site invisible till the time you make it live.