Well, here's what happened. I installed it perfectly into place. Pushed on the corners, and it snapped into place perfectly fine. But then, when trying to place the motherboard on the standoffs, the IO shield pushed against the motherboard, making the holes not aligned with the standoffs but about a couple centimeters to the right. All the motherboard ports are properly in the IO shield holes, but I have to push the motherboard with more force than expected against the IO shield to align it with the standoffs. So, with one hand I am pushing the motherboard, and the other hand I am trying to get these screws in place with a single hand.
Then some of the screws are crooked because it wasn't perfectly aligned, so I have to try again and again. Or I eased off on the force a tad, so I have to restart. Finally after about 10 tries I managed to get a few screws in which kept the motherboard in position, then I could install the rest of them. I don't know if you've ever had experiences like this, but I 100% installed the shield properly, and there was just no possible way to align the motherboard with the standoffs without pushing the motherboard into the shield. I almost actually sweat on my motherboard, fortunately I backed off and the big drop of sweat landed next to the computer.
Unless you can shed some light on what I did wrong, everything seemed perfectly fine to me.