Help with installing Spacebuild 3

I downloaded the svn of SB3 and have it updated and all, but when i select it on the list in singleplayer, when the game starts it spams “Install Spacebuild”
I checked and yes, i do have a SB3 folder with a green check over it, which im assuming means im not missing anything right?
Anyone have a way to fix this? ive recently cleaned my gmod folder and am redownloading all of the major addons.

You put Spacebuild3 in your Addons folder; it’s not a gamemode anymore.

ah thanks