Ur fine dude..my start date for opt was july which would be almost the end of the 2 month grace period..however for some reasons my opt was extremely delayed and i received it on mid Nov with different start and end dates. I was in contact with my international advisor all the time and had been checking to all forums. All of them say as long as no decision has been made in regard to your application you are safe. Hope you didn't start your work before your EAD card arrived.