Lightburn will not recognise my Bedsize correctly

Does your machine have limit switches, and homing enabled? If not, the machine has no idea where it is, so you’ll have to jog it to the front left corner, then power it off & on so it treats that as the origin.

If things are flipped, you likely haven’t set the origin corner properly. You’d do that in Edit > Device Settings. Change the origin to this:

image

You should also read through this: