My entire (butterfly) key falls off, cup included.

A while back, my 'w' key stopped working. I investigated, and it seemed the plastic 'cup' of the key had actually fell off, so I had to replace the entire base (I'm not sure what to call it) using replace my keys - I'm hours away from the nearest apple store with no car.

So I got the replacement, and I had to peel off the base and put down the new one. However, while it's now functional, it falls off incredibly easy. There seems to be missing a 'glue' component of some sort that keeps it on the keyboard.

What should I do?