SOLVED: Thanks to this guy from androidcentral:
"Originally Posted by DBVille: And, make SURE the hooks aren't bent up. I am betting the hooks have been bent up, at least on one side, from trying to push it closed. (dont ask how I know). Look very closely at the hooks. Put your finger nail under them and pry them up/apart from the back if they are too close to the cover to engage the clips on the phone. When done right, it just snaps on. But, you must get the bottom done first."
The hooks were bent up... fixed them with my nails. Now it snaps back on. Still pretty cheap though.