Congratulations for your pi2scart and pi2jamma…
First of all download the image you want to use: (Regamebox, Retropie, Recalbox)
Why use the Images on the site? http://pi2jamma.info/
These have the good config files already done for you. If you want to try make your own configuration you are going to face issues people resolved already..
TIP: even if you are a beginner or and advanced user, we recommend to start with the pre build images and continue developing on them. Instead of starting with a new image and redo all our work.
We encounter many questions about customers who try to do it the other way around and 95% of the time you will encounter a problem already fixed in our builds.