If you haven't already, now is the time to start serious teacher shopping. You might be in a part of the world where you have access to someone who can get you there, or you might be in a situation where you need to consider travelling a moderate distance in order to study with someone of that calibre. If you can find a Curtis grad, or someone who has studied with Edgar Meyer or Hal Robinson, that would be a great place to start. Hal Robinson teaches at the Curtis Summerfest, Wabass Institute, and probably somewhere else over the summer. Edgar Meyer has taught at Aspen for a while, and I assume he continues to do so. While you have missed the deadlines to apply for this year, it would be really great to apply for the summer of your grade 11 year, so you have a chance to work with one or the other before you audition the following year.
If you do not have the opportunity to study with Hal or Edgar directly, or one of their recent graduates, you need to be looking at serious pedagogues in your area. The competitive nature of Curtis has been mentioned before, but you are essentially applying for a position on the Olympic double bass team, as far as competition goes. If you have a major symphony orchestra in your area, get in contact with the principal and talk to them about lessons. If you don't have access to someone like that, find the best local-ish teacher you can, and then strongly consider making biweekly or at the least monthly trips to study with a heavy hitter. While it isn't impossible to get in to a school like that, they literally have the best of the best from around the world applying to study there, so you need to know what you are up against.
Finally, if Curtis is where you are planning on applying, look at the other schools with a similar track record, consider who is teaching there, and what you can do to get yourself to an appropriate level to study at some of the other options. The audition winners list in the Orchestral Auditions section gives you a pretty good idea of the schools that audition winners are coming out of, and if you are planning on an orchestral career, that is worth considering. It is also worth considering summer programs with the faculty at those schools not only because if you audition for those teachers you have a better idea of what they are looking for, but because there are some really great bass pedagogues in North America right now, and having the opportunity to study with any of them for a few weeks over the summer is more than likely going to help with your bass playing.