do both physics and chemistry. it seems that you picked those two because you wont be bored with it and that you are just worried about the challenge. If you do not have the drive for it, you wont do as well so keep both of them.
I feel I am ready. Can't wait to do the subjects I want to do rather than be forced to do compulsory subjects...grr phys ed with psycho teacher:burn: What will you look forward to?:)