Shoulders can't be unusually long, let alone caused by surfing the Internet. It is possible to be influenced by genes, but it is unlikely.

I guess your bad habits and incorrect sitting posture caused the imbalance between your left and right shoulders. One shoulder is high and the other is low, which looks long and short, just like you will bow if you sit incorrectly for a long time. It doesn't matter. Pay attention to correct your sitting posture. You are only 17 years old, and your bones are not formed. Pay attention to the change, and you will correct it.