Whatever happens happens. Just do the best you can in supporting your character and don't leave the match with two thumbs stuck up your ass. Usopp has an infinitesimal chance of beating Bon-Clay. Go into the match with high hopes of receiving as many votes as you can for your character. The more votes at the end, the better you can say you did and at least you tried. If you campaign for as many votes as possible that's the only real chance the character stands to winning the match if he/she is not the favored pick.
Leave the match with your head held high. That's all that matters.
Vote Usopp! ;D