Look closely at that picture you just posted. Do you see the sides of the tray in it?
That is an overlay to make sure that when you place your design on the material, you place it into the area that the laser head can reach. It cannot reach about 3/4" to the left of the overlay, or 1/4" to the right, because the head needs space to decelerate at the sides. There is also about an inch or so along the top side that you can’t see.
This is what the folks at Glowforge see when they take a picture of the inside of the bed.
That wide angle view is corrected using an algorithm with the thickness of the material to give you a more human looking image that they send back to your computer. But they crop part of it off so you don’t place the design where it won’t work.
Or to put it another way, what looks like the upper left corner at the very edge on screen, is actually about 3/4 inches in on the material.
To maximize the use of your material with a Basic or Plus machine, treat the lower right front corner as the origin, and build out from there. The material needs to completely cover the gridded area of the tray, and there will be a band along the left and the top that you can’t see or cut from that postiton. But if you need to, you can turn the material over and use that band up for small cuts later by placing it on the bottom and right side.