@munkylord84 When you say "already built" do you mean you bought a pre-installed RetroPie bundle, or a friend built it for you?
I am asking as in order to troubleshoot the community needs to know details of how it has been setup initially. If a friend has built it, you'd need to ask them so you can pass on the details. If you bought it however, I doubt you'll get much help here as these types of packages are flying in the face of the Devs here making money off the back of their hard work.
You'll be directed to reinstall the official image off the site before we'd help in that instance.
Also, for N64 you'll need to overclock and tweak settings for best results, and there's great documentation on this in the wiki.