Okay so i was told finishing this questline would net me stargate tech. Is that true? cause i just finished it by handing the keys over (mistake?)

Stargate technology is randomly discovered from ruins, and is rare af. That said, as a veteran achievement hunter from steam, I have a predilection for saving my games before choice points like that and reloading them to do things the other way once I've obtained the achievement. I honestly can't recall if keeping the keys from that questline grants stargate tech, but I found it for myself from a planetary survey of 'ruins of an advanced technological society' or some such.

Stargates are an orbital building structure so it isn't shown in the tech list.

You should see them and able to build them when you go to your colony screens now though.