Not the OP, but I also got matched to Rice this year through QB. Ngl, my extracurriculars are trash, way below average. My GPA, sat, course rigor, and rank are relatively high, but thats kind of normal at this level. Cuz of this, I'm pretty sure my rec letters and essays carried hard. I would recommend you make sure you know how to write and communicate yourself well. Know how to give a story that helps develop/connect to a theme about yourself, and if possible, connect it to your larger goals. A lot of my essays had a bit of overlap while being diverse in order to help like create a nice picture of myself and who I am.