agree with Edens' comments, but to add:
Use at least four pins, and pin thru the material and jersey - not just run the pin thru the little hole in the corner. Nothing worse than having the parachute look, plus the fluttering chattering sound as you ride.

here is a handy guide: http://planetadventurerace.com/bike/race-numbers.shtml

lastly, save the tyvek - makes GREAT tire boot material. Just cut into strips and stuff in saddle bag.