One possibility…
If you prefer to work in metric, you will want to create your artboard in Illustrator to 508 mm x 304.8 mm (which corresponds to the size of the bed on the Glowforge) and design your shapes on those.
It’s actually better if you use Save As to save the SVG instead of exporting it, but if you do export it, make sure that Preserve Illustrator Editing Capabilities and Responsive are not checked.
Examples of the correct way to save an SVG for the Glowforge interface are discussed here:
You might want to test it on some cardboard before shifting to another sheet of acrylic. (Not sure if this is the problem, but it’s a possibility. Files that come over from Illustrator are generally not resized if the SVG is saved correctly.)