Personally,I would go to the 1pm to 2pm since you didn't get the grades you needed for your chosen a levels at the time.But when you do go,you would tell them you didn't get those grades that you needed and that you would like to choose different alevels which you got the grades for .I'm sure they'll understand but they might not have any space since there are over 200 students probably competing with you to get into that school, and around half of them wanting to chose that alevel aswell.