Scoop’s installation folder is not listed on PATH environment variable
First of all, have you tried to restart your computer? (logging out and in is enough; that is, if Scoop was really installed in first place)
Second, you can try to install Scoop manually through Powershell:
Invoke-Expression (New-Object System.Net.WebClient).DownloadString('https://get.scoop.sh')
If there’s an error it should tell you 