Why are my wall hooks ending up crooked?
The screws in your picture have a tapered head that match the holes for the screws, so when they are tightened all the way, it will force the screw into the center of the hole; this is why they are OK until they are tightened.  My guess is that your marks or holes are not perfectly in the center.  It could also be that you are drilling at an angle.  Grab a square and hold it against the wall so you can see what 90 degrees perpendicular looks like - are you drilling on that angle or slightly off?