Key replacement difficulty

Second update: seems to be (at least partially) solved. Leaving this up in case helpful for anyone finding this thread.

1. I used a flathead screwdriver to disassemble the replacement key, after lifting it from the keyboard, and essentially start again
2. Resting the plastic cup element in the gap still produced an inconsistent response to pressing the key... until I pressed hard enough for it to suddenly snap into place
3. Once I realised that made all the difference, I prised it back out, put the butterfly piece in first, and then managed to press the plastic cup in such that it stuck
4. And then fitted the key cover on top of that, as normal - starting at the bottom, and then pushing the top until it clicked

It now stays in place and works as intended. The only downside is that the key isn't illuminated... I'm not sure if that's a function of the replacement key, or if I damaged something, or what. Either way, it works.

Hopefully helpful for anyone finding this.

Update!

I found comments under the tutorial saying the plastic bit is indeed glued on and needs force to come off. I managed that, but now two different problems:

1 - the whole key now doesn’t stay in place. There was talk in the tutorial comments about using glue but reluctant to do that if it’s irreversible

2 - it only registers a key stroke when I press the key very very hard.

the picture of the key is the right way up - in case that’s important.

not sure if I need to take all the key components apart again, and if adhesive is advised. Thanks in advance!