Yea I don't think you did. If this card was working fine air cooled previously then the block probably isn't flat unless it's working better now?
I have a reference XG7 for my Zotac 3090. It worked fine with the original paste. I eventually remounted that card with Kryonaut Extreme and only improved 1-2C so the stock paste is pretty good.
You can check flatness with a razor blade like this I think, https://www.amazon.com/dp/B08LYD6645/ref=cm_sw_r_apan_glt_fabc_03GPGJ7M001NPAXNHG11
It'll either rock or you'll be able to see light under it (probably light under it). I haven't done that myself but have seen others do it.
I just use a razor blade. I found a 50 pack on Amazon for like $7 I’ll drop the link. But if it’s not find enough I’ll squish it with a credit card to help break it down blades
Just your standard, single sided blade, like these. Hold it by the thick side, and you can get it almost flush with the plate, and work the sharp side under the model. Oh, and maybe do this pointing away from yourself, to be on the safe side. lol
Use a clean fresh razor blade
https://www.amazon.com/dp/B08LYD6645/ref=cm_sw_r_apan_glt_fabc_YG8VQZJW510Y2GM49WNX