Would this effect the cooling on a Ryzen 3000 CPU? or is the chip in the middle and the edges of the heat spreader don't matter that much?
As others have said should be okay. All the cooler base need to cover is the area where CPU chips are .. and at least 2 outside edges of IHS. Keep in mind that CPU IHS is not really heat spreader as much as it is a load distribution cover. They are sized so their edges are just outside of connection pin area on bottom of CPU and motherboard. This is done so mounting pressure does not flex in the area with all the connections / pins so they don't get bend and not make contact. Keep in mind there are 100's / 1000/s of these connections between CPU and motherboard and all have to make proper contact for system to work.
I don't trust the word of many of the company companies out there. They say whatever will sell product, meaning their word is about as credible to me as a carney barker saying you can't loose. Just look at all the carp pumped out by CLC companies about their cooling ability vs air cooling.