Are you going to be a 2L this fall? If so, then try to write on next year if you can.
There is not necessarily any relationship between being an "A" student and being talented at teaching.
I would recommend to the OP to put the actual class rank, since you know it and it seems less strange than "top 6%" and more favorable than "top 10%". So something like: Class Rank 12/216 or 12 of 216. Congrats!