Gonna tackle this in chunks
I'm worried that my extracurriculars are going to be lacking
Your extra curriculars are a little cookie cutter, but thats fine as long as you aren't shooting for a top 20 school or something. Mix it up with some non-clinical volunteering (Library work, tutoring, fundraisers, soup kitchen, etc.)
I'll perform poorly on the CARS section of the MCAT.
Practice questions. Practice questions. More practice questions. The CARS section tends to be most people's weakness and even more so for someone who is mainly math/science oriented. The consensus seems to be to tackle the strategy behind the questions. When the time comes, do as many CARS practice questions as you can to get a feel for exactly what each question type entails and how to suss out the information from the paragraphs.
You can always take a kaplan/TPR course or something if the above fails you
I should add that I'm the type of person to read through a paragraph and forget everything that I just read.
No you're not. The fact that you have a 4.0 GPA tells me that you retain information well. Its just a matter of fine tuning it so your brain retains non-science/non-math information. Step further: You don't even have to retain what you read from those paragraphs, or even read them at all. I scored well on cars without more than skimming the passage, going to the questions, and then going back to the passage to find the information needed to answer the question. Don't start out thinking like this, its only going to hinder you if you don't believe in yourself. If this is truly a problem you can't get over, try reading a couple of passages out of random books and then re-write them in your own words to see if you understand/retained what that passage was about.
Use your resources. SDN Essay readers, pre-med advisor, other faculty (preferably an MD/DO if there are any), family friends, hell even your primary care doc if they are up to it. No personal essay starts out great, its about improving it over iterations. Start in January of your junior year and that should give you enough time to revise, and perfect it before the AMCAS opens.
Your school should have interview prep, even if its not specifically for medical school, most schools have workshops to teach you how to interview. If not then ask professors, and other faculty if they would be willing. A med school interview is about getting to know YOU and your application. You already have all the answers to the questions they could ask, but it's about learning to present it in a conversational tone. See below for more on developing social skills.
and I find it difficult to sustain a conversation at times since I'm a huge introvert.
I really wish people would stop using "introvert" as a crutch to explain things. I myself am an introvert. Yes I like my comfort zone, and 80% of the time I am unwilling to leave it. But that is not an excuse to not push yourself outside of your boundaries and develop socially. I had this problem too, until I said screw it and jumped into things with both feet. Join a club, even if it's just a movie club where you sit around and watch movies with people and then talk about the movie. Get a job where you HAVE to talk to people (because lol thats what most of being a doctor is anyway) I became a tour guide for my school even though I hate the sound of my own voice. You're going to hate it as an introvert and want to retreat to your safe space and guess what? YOU CAN! At the end of the day, your comfort zone/safe space/whatever is always going to be there and you can always go back to it whenever things get overwhelming, but the opportunities to grow and learn as a person are not always going to be knocking at your door.
Overall I think you're in a good place and on the right track, you just need to believe in yourself a little more and stop with the self-defeat before you attempt anything. Starting out from a negative place is going to make it harder to end up in a good one. Many people in your situation (bad with CARS, introverts, socially awkward) make it to medical school all the time, there's nothing stopping you from being one of them.
