What can I do to improve my chances of getting into top tier schools if my stats are not the best as a freshman?

The good news is that, out of all your high school stats, your freshman year is the least important to colleges. So you have plenty of time to improve, and if you do, colleges will put more stock into what you do in your sophomore and especially junior years than freshman year.

For extracurriculars, you should really just try to join some different clubs, teams, do volunteer work, work a job, etc. Any of those things, or a combination of them. Find some things that you're interested in doing and pursue them consistently over the next two years—if you do, you might end up with some responsibilities or a leadership position, which is what colleges really look for. For ECs, "getting your stats higher" is really a function of effort and a willingness to put your time into these activities.

For your PSAT score—first, the PSATs aren't part of any college applications. They're meant to be practice for the SAT, which is what actually matters. If your PSAT score is low as a freshman, that may first be because you haven't learned everything on the Math section yet (since some of that material is taught in classes you'll likely take next year). So study and go through your classes normally, and you should see your score rise. Otherwise, look into doing SAT prep work or courses—even the free ones available from Khan Academy are a fantastic resource.

Hope that helps!

You've got lots of time to get things figured out so try not to stress too much! Like @jcdenton mentioned, colleges care the least amount about your freshman year grades. Some schools may not even consider them at all. Try and determine why you feel like you are struggling this year and plan to make adjustments where possible. Is the work too hard? Or is there too much of it? If that's the case, focus on getting organized and setting a schedule for yourself. Block out dedicated time for homework, studying, etc. Find a dedicated place to do your work too. Make sure you stick to your schedule as best as you can and work from the same place as much as possible.

For ECs, what do you like to do? Find some activities that are related to what you're interested in and pursue them as best as you can. Colleges like to see dedication to ECs but also what type of leadership or responsibilities you have within the activities you do. Don't worry about having all your ECs related to your interests, schools prefer students who have varied interests.

The good news about PSAT is that it doesn't matter for schools. The real deal is the SAT and you have plenty of time to study for that. Like @jcdenton mentioned, you might've scored lower than you wanted because you haven't learned all the material on the test yet. cracksat.net and crackact.com are both great sites for practicing for the SAT/ACT. They've got lots of practice tests of stuff and I recommend checking them out!