I would...
1. work on solving simple tactics puzzles with a high consistency
2. read over some master games in your openings
3. cut out blitz until after the tournament
Do NOT think that the big money prize is yours to lose. That is sabotaging yourself psychologically. Be happy that you have the opportunity to play for such a large prize. Just because you have the highest rating in your section doesn't mean you'll be the 'best' player. A ratings difference of 10 points or so is basically meaningless.
I am currently rated 1599 and will be playing in the World Open this July. I will be the highest rated player in the u1600 section. I normally, play in scholastic tournaments, so this will be something new. I am competing for $15,000. HOw would you best suggest I prepare for this tournament. Please Help ASAP!!!