Hi @kitkat20,
The bolts provided for installing door handles are designed to work with doors of different thicknesses. They usually have 2-3 grooves in them where they can be cut for use with different thicknesses of doors. If you've tightened them as much as you can and the handle is still not sitting tight with the door, I'd say the bolts need to be cut down.
To do this, take the door handles off and use a pair of end cut pliers to cut the bolts down, using the grooves as a guide. You'll need to apply a lot of force to cut them, but it is the best way to do it without adding burrs to the bolt. It is hard, but it will work, trust me, I've done it hundreds of times.
If you've got a hole that is too big for a screw, the classic trick is to grab some toothpicks or a dowel and use some PVA glue to glue them in the hole, then snap or cut them off. This additional timber will fill the hole just enough for the screw to bite.
Let me know if you have any further questions.
Jacob
