Hey olivia,
I disagree with what people are saying here.
From what I can see, you probably think that you're "skinny fat" where you're skinny, but covered in a layer of fat (not too fat though)
What you need to do to shape up your body and give it the lean physique that I believe you are looking for is to incorporate weight training into your lifestyle.
Trust me. There's nothing sexier than girls who lift weights. So be confident, go out there, and do some resistance training!
Cheers