A couple of possibilities come to mind...
The handle which was difficult to install is either the wrong part or, defective so that it is holding the cartridge partially open. Remove the handle and push the cartridge to the full off position and see if the drip stops. If it does the handle is the problem.
The difficult handle installation broke the cartridge, and the cartridge requires replacement. If the cartridge requires replacement check the handle carefully to make sure that it does not damage the new cartridge.