Could Ears Change Shape From Wearing Headset?

While anything is possible, it would be extremely unlikely that wearing any sort of headset as a teenager would affect the shape or position of the ears. It is more likely that asymmetries are simply being noticed now that weren't noticed before. In young infants, the ears can be molded or shaped with long-lasting results, but these tissues are soft and pliable. In older children and adults, we know that the ears cannot be easily reshaped without surgical intervention.
Best,

Thanks for this interesting question.  Once you are out of infancy, your ear shape is pretty much permanent.  Only in the first weeks of life can the ear be molded.  When you take your headphones off, you should notice that the ears return to a stable position.  You have likely been wearing them so much that you have not really noticed their baseline shape!   Also, the headphones should be applying equal pressure to both sides, so this could not explain the more prominence that you notice on the left.