The reason why the mouth becomes convex:

According to your situation, I guess your teeth should be a little crowded before correction.

Girl 15 years old, generally has passed the peak growth period. The length of alveolar bone (teeth grow in this bone like radishes) has increased very little and can't accommodate so many teeth. In this case, in order to align the teeth, only the teeth expand outward to make room. That's why your mouth is protruding now.

Solution suggestion:

Is your face round or long? If it's too long, you can choose tooth extraction correction, and pull out four four teeth (four teeth are the fourth teeth counted backwards from the front teeth) to make room for which front teeth make your teeth protrude backwards, so that after the teeth move backwards, your face will not look so convex, and it will also make the long face a little shorter and make your face more harmonious.

If your face is round, I suggest your dentist take a look at your mandibular angle (I won't explain what this angle is, your dentist knows it) to see if you are suitable for tooth extraction.