I'm not aware of any Long-Screw issues with the iPhone 7. That happens when you over tighten the screws for the screen assembly bracket. That said, think back to when you re-assembled the device. These screws really should not be tightened down with any force.
The other possibility is that you may have damaged a flex cable. These can tear quite easily. Look at them again under magnification to see if there is any damage.