As a Texas student looking to apply at UT Austin as well (dream school is MIT but like yourself, I don’t know about that), I’ll give you advice off of what I know.
First, I would like to address that it is not to early to worry about how to advance through your high school career. In fact, it’s rather envious that you are taking the initiative and preparing now. First, I would say you are off to a great start. You definitely started off better than what I did, and if you keep up the way you’re going, you will definitely be admitted into UT Austin. It may be to early for me to claim you’re doing good, but just keep your grades up, be consistent and seek to gain a higher position in your ECs, and you should do fine.
I’m not sure how your school functions exactly, but I would recommend taking Geometry during the summer in order to take AP Calculus your Senior year. If you want, Also consider taking Pre-Cal the summer before your Junior year so you can take AP Cal during your Junior year, then with that knowledge of Calculus, you can proceed to take AP Physics C Senior year. Either take the classes (Geometry/Pre-Cal) during the summer (which could be expensive) or study the subjects yourself (many great FREE online resources to aid your studying) and earn credit for the subject through CBE (Credit By Exam). I give you that information because UT Austin is known for its science programs leading me to believe you’re headed into a Science or Math major. If you’re attending UT Austin for other reasons, then ignore the given information about the summer math classes.
I would also recommend you create a high school course plan so you can have an idea of what you want to take and when you want to take it. This is also good so you know if you have room for certain electives that you would like to take and keep track of how many credits you have collected and how many you have left. Starting your Junior year, began studying for the ACT and SAT tests to prepare yourself to take the test during your spring semester of your Junior year. Taking the test this time of high school is best; the knowledge you’ve accumulated throughout your Junior year will be of use, and if you don’t do too well, you have time to retake the test(s) your Senior year.
Also, don’t be afraid to dive into any Dual Enrollment/Dual Credit programs that your school has. It may not be the “gold standard” AP class that is the common throughout schools across America, but there are many classes available through DE/DC versus AP. Also, while accumulating AP classes is good, taking a different approach can be beneficial as it makes you appear “adventurous”. It shows your readiness for college by taking advantage of whatever is available to you.
To elaborate on ECs, don’t worry about what appears more “prestigious” on a college application. Do what you enjoy doing; your youth is finite. If you’re enjoying what you’re doing, better positions become available to you as a consequence to your participation.
Use a planner. It’s good to create an ideal high school curriculum for yourself in terms of what you want to do each year, but with that long-term goal in mind, it is essential that you break it down into smaller short-term goals. Using a planner is a great way to help you. Trust me, our school has provided one for each student and while most of my peers find it tedious, it has helped me tremendously. Use a planner/calendar, and write down what needs to be done on a monthly, weekly, and daily basis. Having planned what you want to do is good, but actually getting it done is a different story. Having yourself organized, having your time managed productively, and follow through on your short-term goals are a great way achieve your ideal high school life which raises your chances of getting admitted into UT Austin. A simple planner is a great way to manage yourself.
If you have any questions, just ask away and I will answer to the best of my abilities and knowledge.