When you say you are about to burn and you see that it’s huge, are you framing it and seeing the line larger or are you lasering it?
Here is a post on our forum with a similar issue: Framing using a Galvo Laser is larger than the size of the image
Here’s a video that shows you how to calibrate your lens: https://youtu.be/x08cRPkyToc?si=BehQxRcOTIO0zTgv