I signed up for a 7 day free trial online and it's activated but I can't either login online or my roku on my tv when I go on the paramount plus app on my tv.
By "signed up ... online" you mean directly with Paramount+ on their website, right?
It's been a while since I registered with Paramount+ so I don't really remember but ...
Try going into the Paramount+ app on your Roku and clicking on a program to watch. I *think* it will then give you the option to either subscript or sign in. Sign in with the credentials you originally set up with Paramount+. (Some channels do it this way, but I can't recall if Paramount+ is one of them.)