On one hand, I as well as others would be disappointed for going back on my word. But on the other hand, i feel like people will be disappointed that i finally play people like m2k, zenyore, and revan just to end up using secondaries. And on top of that, I im gonna be disappointed in myself if think i could win and end up losing.
So much disappointment coming from both ends.
The dilemma is strong.
Not the kind of mentality I'd expect from someone as optimistic as you. Regardless, you won't know unless you try locking with Fox and seeing how well you perform. I'm sure you didn't come this far with all your training with Fox just to ditch the character for two other characters considered "superior" by many, let alone characters you don't personally even enjoy using other than to win, simply because you don't feel confident that you'll do well. Who knows, you may even win this tournament with Fox, after all.
You should be going to this tournament with the mentality that you are going to do your best and having a great time with Fox, regardless of the outcome. Besides, you'll only improve your skills in this tournament, even if you lose, anyway, and, of course, the more you improve, the more likely you are to win tourneys in the future. Nevertheless, it's up to you, so choose what you'll enjoy the most. Hopefully, that helped (or probably not).