Will I get into the Ivy League (Brown University PLME) with a good SAT, excellent junior year, but bad freshman?

PLME is one of the hardest programs in the country to get into. It has an acceptance rate of just 3.6%. Your standardized tests are good, but improving your SAT will go a long way. Brown uses Superscore, which means you can keep your English score and can focus on getting your math up. Your GPA for junior year does a good job making up for what you lost in your freshman year, but it might be difficult to come back.

The biggest problem here is your extracurriculars. You have some that you have devoted a lot of time to, but not all show a desire to become a doctor, to help people. Remember, being accepted to PLME means that you will be a doctor in 8 years. They need to know that you are not going to take the seat just to change your mind. Look to see if you can devote some more time to volunteering at the hospital. During the pandemic, you can also act as a remote volunteer for the American Red Cross. Look up other activities for pre-med to see what else you can do.

I wish you the best of luck on all future endeavours!

Here's the thing about PLME and similar programs (like Northwestern's HPME and the BS/MD programs at BU, Case Western, WashU, and other highly ranked schools). They more or less require students to have significant extracurricular experience in the medical field—not just a little bit of volunteering, but actually shadowing doctors in hospitals or clinics and getting as hands-on as allowed for high school students in medicine. This is because, as @desaisiddharth said, they're admitting students to their medical school alongside their undergraduate colleges. They need to be absolutely sure that you're not going to change your mind and go off to study something else. Right now, that kind of experience is where your profile is lacking.

On the flip-side, your academics are fine. BS/MD program admissions aren't as competitive as they are because they require absolutely perfect academics—they're as competitive as they are because they require students to have demonstrated a clear and indisputable interest in medicine in a part of their academic careers where that's not an easy thing to do. A 1550 should be enough on the test scores front that a higher score won't particularly help you, and you absolutely do not need to take any more Subject Tests. 3 Subject Tests is typically the maximum useful amount for any college, and if you send more than that it typically won't help your case any more than those first 3 would have. Bio M, Chem, and English would be a strong selection to send to a BS/MD program (shows clear achievement in sciences but also the range to do well in humanities; I wouldn't send Math 1, as it's typically viewed as relatively basic exam in comparison to Math 2 by advanced schools and programs). Taking the Physics exam at this point would not be a good use of time. Just send the 800s on Chem and English and the 790 on Bio M.

Your GPA is also in okay shape—I don't think it will hinder you that much, because colleges typically put a significant amount of positive emphasis on an upward-trending GPA. Considering that, your cumulative unweighted GPA after your first semester of senior year, if you keep up this level of performance, should be about a 3.7~3.8, which should be above or at least around the academic cutoff for these top-tier schools. In short, your academics are not going to prevent you from having a chance at PLME.

What you need to do now, if you're serious about PLME (or BS/MD programs in general), is get experience shadowing doctors, volunteering more extensively in hospitals or clinics, or otherwise pursuing medicine in some way in the 7 or so months you have until these applications will be do. There's good news and bad news on that front. The bad news is that many typical opportunities along those lines will be difficult to come by in the present environment. The (ironically) good news is that living in the midst of a historic pandemic should give you the opportunity to volunteer remotely and assist in relief efforts in a particularly novel and unique way. It wouldn't surprise me in next year's application cycle to see BS/MD programs look very favorably at students who use COVID as an opportunity to deepen their experience with medicine and use their free time and effort to help their communities through this crisis.