Dear Marietta,
Before reaching adulthood, your fat cells will continue to undergo the appropriate changes that will fit your body and its needs.
As a maturing teen, you need to let nature take its course according to its laws and regulation within a healthy margin.
If you were to remove the undesired fat cells at the age of 13, in best case scenario more will grow and will tend to replace the ones you have lost; it is possible that some fat cells would grow replacing the removed ones asymmetrically.
That said, I recommend that you exercise and diet in a healthy manner to achieve your desired goal reasonably.
Thank you for your inquiry.
Best of luck to you.
Dr. Sajjadian