You're really cute! I think the basic details of your costume are really nice. If you're interested, I have a few tips that might help you achieve the "look" of the character better. I noticed that you are pretty petite. I think there are a few details of this cosplay that are working against you, rather than for you. Fortunately, they're super easy to fix and will actually help you achieve a closer resemblance to your reference image. =)
So, to create the super long legs that she has, try boots with a little heel on them and make sure that the tops don't go more than an inch above your ankle. The boots in the photos you posted are flats. In the reference image Serrah actually has little wedges. Finding the right shoes is really difficult so if you can find something at the thrift shop with the right heel, you can use this awesome tutorial for boot covers:
For the leggings, make sure that they land mid thigh rather than just above the knee. Just above the knee gives the leg a very cut-off look. A really easy and cheap cheat for the thigh-high stockings is to buy an inexpensive pair of black leggings and just trim off the leg pieces to the desired height. To keep them up you can use sock glue or Top Stick.
I would suggest making your silver garter pieces about half their current width. By making them thinner, you are again helping your legs look longer and staying more true to your reference image.
lastly, I agree with the above comment about a shorter chain on the necklace and posing energetically. You seem like you probably have a really cute personality; don't be afraid to make big gestures. Everything looks smaller in a photograph so make sure that you stand/sit straight and really make your gestures big and cartoony. It will feel very weird at first but it really just makes you look comfortable in pix. =)
I hope you find my comment useful. Keep on rocking the cosplay scene, I can see a lot of potential in you.