Two other unsolicited but hopefully helpful pieces of advice:
1) If you are involved on the technical side of the team (and/or if you do technically creative things outside of FIRST), consider submitting a supplemental maker portfolio:
https://mitadmissions.slideroom.com/.../program/21846
2) KEEP YOUR GRADES UP. It's not uncommon for FIRST students to sacrifice their grades for FIRST. Doing FIRST is great - see this
essay our dean wrote - but colleges generally won't accept it as an excuse for poor grades. Learning how to do *both* well is a key signal to college that you've got time-management down.