It's unlikely that stopping chewing gum will make your jawline significantly smaller.
While chewing gum does exercise your jaw muscles, it's not a significant enough workout to cause noticeable changes in your jawline structure. The muscles in your jaw are relatively small, and they don't contribute significantly to the overall shape of your jaw.
The shape of your jawline is primarily determined by your bone structure, which is largely genetic.
If you're concerned about the appearance of your jawline, consult a healthcare professional. They can provide personalized advice and recommend appropriate treatments if necessary.
