I gotta say that you did an awesome job for your first con cosplay. Even though you can improve aspects of the costume, it still looks like you put a good amount of effort into what you wore. I like that you actually made big snake earrings.
The first thing you need to do is get a good wig. Even if you cut your hair into Boa Hancock's style, a wig is still easier to deal with in the long run. It's often harder to maintain natural hair throughout a convention day, and often it will go flat or become unstyled. This also saves you time when it comes to putting on everything and looking good before you head out in costume.
Also, when you rework your sleeves, you need to make them more like bell sleeves on the bottom. The color of the designs at the cuffs should also be more of a gradient, and the lines of your shirt designs should maintain some consistency - if you use black outlines on the sleeves, you should also do black the outlines on the collar.