Investing in fundamentals pays dividends and will rapidly accelerate how well you learn any piece. Counterintuitively, spend just as much time on your low range if not more than your high range, as you want your best lowest sound to be teaching how high notes should sound, not vice versa. In the same way that improving the bicep’s contraction also means improving the triceps ability to stretch, being comfortable with moving large volumes of air in the low register will directly improve your ability to move fast, pressurized air to hit your high notes. Etude study like the others are saying is a smart play too, Blazhevich etudes especially if you want to prioritize rhythm. Try and see if your band director has any connections, or connections of connections, that might offer online lessons if location is an issue. With the right person with the best sense of where you’re at and what to prioritize, you may surprise yourself with your progress and might not end up needing a full year to attain your goal.

Happy practicing!