I think that if your PSU hasn't broken yet, it probably won't until it ages and dies like all other aged psu's. And the pcb inside the PSU is a little less fragile than for example a motherboard pcb. Which means you have to damage it quite badly for any effect to be seen.
Of-course you could get really unlucky, but I think you'll be fine. And If it would break, I think Corsair won't accept a RMA, as they would refer to "user caused damage" most likely.
About the screws, were there no screws that came with the PSU itself? They could be shorter than the ones you have. If there were screws that came with the PSU and they were to long as well I think Corsair would be happy to get to know about it as it would count as a construction fault.