To ensure your LightBurn workspace matches the physical size of your laser, click the ‘Spanner/Screwdriver’ icon top-center of the main screen to reveal the ‘Device Settings’ window where you can enter the size values. (Screenshot is an example only, enter your correct data)
You can control the ‘Units’ of measure used in LightBurn to help with this. Click the ‘Gears’ icon top-center of the main screen to reveal the LightBurn ‘Settings’ window.