I know a lot of Houstoners. Depends on the rigor of your high school course load also, since there's a lot of applicants from that area.
Lab experience and shadowing will be a plus, and the teaching also, but what constitutes "average" GPA? You'll need to clarify that, because in theory, a 2.0 is "average" since C's are "average." If you're applying with C's, it'll be very difficult without other supplemental factors to bolster your application.
The only thing I can say is your SAT score is average to slightly above average for the competitiveness of a top 20 school. We might have a higher acceptance (20% vs 7%) compared to somewhere like Harvard, but that's not indicative, since it's still a low chance.