jorjaiso,
After carefully examining your photos, I see the flaw on your backpack. I also understand the frustration you are experiencing. It reminds me of the first time I noticed a minor rock chip on my car, and the big mess I created with a paint repair kit.
While I would be bothered by the flaw, whether it is major enough to cause me to return the backpack would depend on my plans for it.
It took me some time to get over the rock chip and paint repair mess on my car, but it no longer bothers me. Now, it is just a funny story, and the car has dozens of rock chips. I had to tell myself that my car was NOT a museum piece that could never be touched or driven. Instead, I purchased it because it enabled me to drive where I needed and wanted to go, and rock chips are part of the cost of the enjoyment I get from driving it.
So, the point I am trying to make is: If you purchased the backpack to keep it encased in glass, then yes, I would return it. However, if you plan to use and enjoy it; I would not let a flaw that only you will see keep me from using and enjoying it. With use, it will get additional flaws.
Finally, Congratulations on your new backpack!