I don't think that cosplay judges are going to judge harshly based on the fandom. You should enter the competition to have a good time and build up your confidence - nobody is going to boo you or bar you from entering with a costume like Jade's dress.
Most of the cosplay judges I've met don't let their personal opinions about a series interfere with their job as a masquerade judge. If you have the most impressive/well tailored costume, you should win a prize. It's that simple. The judges all have experience with fandoms of different varieties, and for the most part will judge objectively based on costume/performance. I've spoken to judges who have begrudgingly given out top honours to a costume that was from a fetish anime (the costume was tame and G rated) simply because the craftsmanship was exquisite, or conversely given out prizes to characters that they've never heard of before the masquerade because of a great performace.
Equally, if you don't win a prize then don't blame it on the judges' dislike of your fandom (as I have seen happen sometimes - it isn't pretty for anybody involved).
Regardless, I hope that you do decide to enter, and have a wonderful time at your convention!