I had to work at mine a bit, but I was able to finally get them secured down. I actually ended up using a small pliers to pull up and turn the twist-lock mechanism while at the same time pushing down on the mat to get the the twist-lock up far enough to clear the mat and lock it in place.
You won't need to use a lot of force with the pliers... just enough to get the twist lock up far enough to turn and lock in place.
Been very happy with my Husky Liners thus far. Good luck.