iMac does not turn on after adding compatible memory card- ant help?

I got iMac 27inch, 2020 model:

3.6GHz 10-core 10th-generation Intel Core i9 processor Turbo Boost up to 5.0GHz

8GB 2666MHz DDR4 memory

Radeon Pro 5700 XT with 16GB of GDDR6 memory

and have a compatible memory card to boost RAM. There are 2x 4GB memory card installed as a default and 2 slots available for me to fill so I got a Crucial 32GB DDR4 2666 MHz SO-DIMM Memory Module(confirmed already it's compatible), and my iMac does not turn on.

First of all, how can I tell memory cards are installed properly? I checked the memory when it turned on without the added memory card and it seemed it's only recognizing one of the default memory card as it says it has 4GB memory which is alarming as well.

Also, should it be 2x 32GB memory card instead of just one?

I hope all of these makes sense.

Thanks in advance!