After changing WordPress address and site address, I’m unable to log in

I’ve been tasked with completely renovating an old site someone gave me. Earlier today I installed a few plugins, backed up the old version of the site, and put it into maintenance mode. The site was at samplewebsite.com, but it would always redirect to blog.samplewebsite.com. I wanted it to just be at samplewebsite.com, so I tried to fix that. In the WordPress dashboard general settings, there are options to change the WordPress address and the site address. They were both set to blog.samplewebsite.com, so I changed them both to samplewebsite.com. When I saved those changes, I was kicked out of the dashboard and any attempt to log back in was met with a blank white screen. The maintenance page is still there on the website, but everything has been shifted to the left side of the screen when it is supposed to be centered. What appears to be the problem here? How would I fix it?

Thanks.