Don't try and stress about it too much as nearly everyone gets really bad grades at the start. But make sure not to get too relaxed as that will most probably lead you to failing at the end of the year. What I would suggest is revise during the half term for at least 4 days and catch up on the things you don't understand. With A Levels you're not really allowed to rest so just pick yourself up and use those bad grades to encourage you to not get them results at the end of year.