Download @BillieRuben kerf tool and use it… 
Your description should also work.
I have to agree with @RalphU that Lightburn is working correctly. There are a bunch of users that have used and still use keft settings.
I use mm, so the numbers look off to me and I’m too blind/lazy to convert them, however, it seems to me that the kerf on my 3mm acrylic and mdf was surprising larger than expected… I’m still looking for the files after a new computer upgrade.
To see if it’s following the drawn line, you need a kerf setting the same size as your lasers kerf.
Good luck
