At least in our experience extracurricular activities (ECs) are important for a small number of very selective universities (Harvard, Stanford, MIT, …) that are choosing from among a long list of applicants with nearly perfect grades. For most very good more normal colleges and universities (perhaps ranked below about 20 or 50 among the thousands of colleges and universities in the US) ECs are not as important.
One daughter had almost no ECs at all prior to her senior year of high school. She also values her free time. She was accepted to every university that she applied to. She did not apply to Harvard or Stanford, but that is okay. Where she applied were schools that were a good fit for her.
You are most likely not applying to top 20 universities anyway.
There are many, many very good liberal arts colleges in the US (and a few more outside the US).
There are a lot of introverted people working in high tech, as well as in biotech.
You should not and do not need to misrepresent anything.
Try to keep your grades up for the rest of this year. Treat people fairly. Look for colleges that are a good fit for you, and make sure that you apply to at least a couple of safeties (where “safety” means that you will get accepted, you will be able to afford to attend, and you will be willing to go there).
I would not worry about a lack of ECs. You do you, and look for a school that is a good fit.