I think I just blew my diet!?

Calm down! It honestly doesn't matter if you have 'blew' your diet. You went over 300 calories; it's not going to kill you! What should you do? Chill out, and start over again and better yet, don't obsess over calories. As long as you aren't consuming any more than 2000 (2500-3000 if you exercise) then you have no need to worry. Overdoing it in moderation is not the end of the world.