I recently bought a CAI WASR10 AK-47 and wanted to add a scope to it. So I bought a receiver cover with rail mounts on it (Like this) When I tried to put the receiver cover on it was too long to fit correctly (by a few cm). My question is how do I fix this? Do I need to file one end down? If so which end? Or should I just get the side mount and leave the receiver cover alone? Thanks for any help.