Did you import a configuration file provided by xTool when you first set up your device profile in LightBurn? If so, you will have a ‘Laser pointer offset’ in your Device Settings (‘Edit’ > ‘Device Settings’) to compensate for the difference in distance between the crosshair pointer on your laser, and the location where your beam will actually fire. That could account for the discrepancy you’re seeing.
You can try turning that offset off and using the ‘Fire’ button to frame instead.