As MacBooks have an aluminum body compared to other laptops, they are prone to scratching. From the pictures, it doesn't look like it is a scratch or dent, so try cleaning it in accordance to the following guide, so as to prevent any further damage:
How to clean your Apple products - Apple Support
It is completely normal to get a scratch every now and then on your laptop, it's part of the process... If you find that you cannot clear it, try to at least get used to it, as it doesn't affect how the laptop functions in any way. If you want to prevent any further damage, you can get a MacBook case. They come for a relatively low price, and it really pays off.