Sadly a lot of random woods will have fillers or glue that a laser has a harder time cutting through. You’re going to need to test - or run multiple cuts to succeed with it.
You can always tell it to run the cut again before you move the material.
If you’re not yet using something to hold the material to your bed, then may I suggest cutting some of these: Honeycomb bed holdown pins. Then when you’re done with your first cut you can reach in and try and pull it out - if it doesn’t come cleanly then close the lid and hit print again (don’t adjust anything). As long as nothing moved it’ll cut in the exact same place again.
As far as selecting a material - you don’t have to select a PG one, but you do need to enter settings. There’s an area for Uncertified Material where you can enter the height (1/8"or 1/4" or whatever) and then you have to click on the operations and enter settings - speed and power. Read about those here: https://support.glowforge.com/hc/en-us/articles/360033633574-Working-With-Manual-Mode
Once you understand Manual you can run tests to get the perfect settings for your material:
Fingers crossed for you!