You don't have to worry about your SAT score or ACT score.
http://www.collegeforalltexans.com/index.cfm?objectid=6D0B8C2F-C987-12B0-27CAFED91FACC7FB
If youre in the top 10% of your high school graduating class, youre eligible for automatic admission to any public university in Texas. To meet the requirements for automatic admission, you must:
Graduate in the top 10% of your class at a public or private high school in Texas, or
Graduate in the top 10% of your class from a high school operated by the U.S. Department of Defense and be a Texas resident or eligible to pay resident tuition;
Enroll in college no more than two years after graduating from high school; and
Submit an application to a Texas public university for admission before the application deadline. (Check with the university for specific deadlines).
If youre admitted to college through the Top 10% Rule, you may still be required to provide SAT or ACT scores, but these scores are not used for admissions purposes. You must also take the THEA test, unless youre exempt from the test requirement. Be sure to check with the school's admissions office regarding THEA, SAT and ACT requirements. (For general information on SAT, ACT and THEA, click on The Tests Youll Need.)
So the goal is to get into the top 10% so you you get automatic admission. To get into the top 10% you need to take AP classes to bump up your gpa.
Also, college applications ask for your class ranking. If they didn't look at it as a factor for admission, they wouldn't need to ask for it.