Ok. Just confirming.
You can try a few things:
1. Try to gently twist the water block.
2. Failing that, try to reheat the CPU or use something like a hair blow dryer.
3. If there's a gap, try taking a syringe with 91% Isopropyl alcohol and squirt a bit into the gap. Let it soak a bit (5-7 mins) and try wiggling it again. If it's working, you can slowly reapply more.
Don't do #2 and #3 simultaneously.