Unsuccessful finish page

How would I go about making a finish page to display if the installation was not successful, at the moment, even if i dont install anything, it will still take me to the finish page, saying that myapp was installed successfully even though nothing was installed.

I have a few sections that would need to link to this page, such as, if a registry key exists then it means its already installed, therefore go to the unsuccessful finish page which says "MyApp is already installed" or something like that
Cheers

You can use Abort to Finish.