You got that flipped.
At no point in your high school career should your goal be “get into a T20 school”. That is a really bad idea.
To begin with, why? There is no reason for you to believe that any of these colleges would provide you a better education and a better experience that any of 100 other colleges in the USA.
Second, most applicants, no matter how good, are rejected from the colleges with the lowest acceptance rates. Wasting your entire four years of high school trying to curate yourself into the “right” applicant, is sad even if you are accepted to one of these colleges. Since you are more likely to not be accepted than to be accepted, that’s even sadder.
Third, admissions is such a tiny part of college. Things don’t suddenly end when you’re accepted. Your life won’t suddenly be better and your path won’t suddenly be clear, just because you were accepted to a “T20” colleges. That is just the beginning of of college, and college can go many ways.
Finally, “T20” colleges, by any definition are extremely different from one another. It’s like walking into a shoe store and telling them “I want to buy shoes, I don’t care what type they are, or what size they are, so long as they are name brand and are expensive”.
Figure out what interests you and pursue it. If you really want to engage in research experience, that do so. However, don’t try to engage in research because you believe that it’s what “T20” colleges want to see.
“I want to work in molecular biology” is a much better goal. getting there through a T20 colleges is just one of many possible paths that will lead you there.
Are you indeed interested in molecular biology? Is that what interest you? Do you read popular article about it and find them really interesting?
If so, then you should explore molecular biology. However, “molecular biology” is a vast field, covering many many sub-fields. Now, for a college major, “molecular biology” is enough. However, if you are looking for research opportunities, you need to know what interests you in molecular biology.
You should also, as @sgopal2 advised - speak with your science department, particularly with a biology teacher. See what the school offers, and what connections the school has.
As others have written, your lab experience is most likely to be in your high school - many have program like AP Independent Research. However, if molecular biology interests you, reach out to faculty at any of the nearby colleges. Many will be happy to take the time to talk to you and help you explore your interests.
Is your GC telling you to take 5 APs as a Sophomore?