Just like your mouth does not change when you eat, even If you take HUGE bites, your vulva does not really change due to sex or masturbation. What you are describing sounds like a beautiful adult vulva.
I am not trying to shock you, but your whole body is asymmetric. Your left and right side of your face looks differently. If you know photoshop, or you have a friend with photoshop skills, cut a picture of your face in the middle, and mirror the halve that is left to form a fully symmetric face again. You will be shocked by the way that looks - nothing like you.
This is what makes you a unique young woman. Three other places where you can see large differences between your left and right side:
Your breasts (one can be a full cup size different). Your nipples are most likely slightly different, and offset differently on your breasts.
Your feet - one foot can be as much as a full size different.
Your vulva - your inner lips can be different lengths, colors and shapes.
An adult woman's vulva will seldomly look like the photoshopped vulva of a porn star, or the closed and nicely tucked in vulva of a young girl.. Very little of what you see in porn are real. They cut and splice, use lighting and camera angles, manipulate videos and pictures! Use cosmetic surgery.
In real life, our outer lips can be flat or bulging out. It can be more forwards, or more to our behinds. Our inner lips can be totally hidden, peeking out, sticking out or hanging out. It can be whitish, pink, red, dark wine red, dark purple, dark brown or even very close to black. It will often be colored differently on the edges.
When we get sexually aroused, everything changes shape. Our lips swell up and seperate slightly, our inner lips heat up, change color and swell up.
This is all normal.
What is not normal is for you to measure your self worth by how your genitals look. They have a very special role. They are there for your pleasure and for making babies. There are no Miss Labia, or Miss Vulva competitions. Thay are a part of what makes you unique and different from other women.
Young men are just as insecure about their genitals. They are worried about size, color, snap, how it bends, if they can get it up, if they can last long enough to please you.
It is normal for you to feel insecure when you share your body in an intimate way. It is something you will get over pretty quickly though. You should measure your self worth on what you contribute to society, on giving your best in whatever you do, on being the best friend, girlfriend, daughter or mom you can be. What you look like under your clothes have nothing to do with your self worth, or your desirability.
So what can change the shape of your vagina? Being overweight can do it. Pregnancy and natural child birth are also likely to change the shape. There is however a set of exercises you can do to keep your vulva and vagina in shape. Use the google and look for 'kegel exercises'. Get into the habit to do it as often as you can. It will improve your genital health, or it
Take care!