It clicked in easily, but I forgot how exactly I did it. It actually pops out if I flip it down while it's moved fully to one side - I forgot which. Moving it to the other side it's quite solid though!
I left it as is, since I didn't have good sand paper nor any colors. It's not perfect, but I was only going for "functional" anyways.
Thanks again for making the model! By now, I have my own 3D printer, and hope to be able to contribute similar designs to the community in the future. So far, I've been mostly printing non-computery parts, but eventually I'll come back to the original idea that made me buy it, and use it to fix broken computer plastics!