I have a motherboard that I accidentally slightly scratched at the very bottom near a usb pin header. I can't test the motherboard to see if it still works because I don't have all of the parts yet. Would that one scratch ruin the entire motherboard if its not even close to any of the crucial components?
Honestly, it depends upon the depth and severity of the scratch. If you have a powerful magnifier, you can try to see if you've scratched through any of the embossed lines. Other than that, I guess you can give it a try and simply hope it isn't too severe
Unless the impact is strong enough to crush the FR4 layer between planes or whatever caused the scratch was sharp and hard enough to gouge through the coating and traces below it, the damage is most likely cosmetic.
You can put a drop of rubbing alcohol over the scratch to 'hide' the scratch while you take a look at it with a magnifier to make damage easier to assess.