It's hard to recommend subjects when we've got very little to go on.
Chemistry at A-level has a pretty big jump from GCSE in terms of the depth of what you learn - especially since GCSE knowledge won't help as much, since some of what you're told at GCSE is either false or vastly oversimplified. If you truly want to learn more about this subject then go for it, but don't go into it uninterested.
I don't really know anything about A-level psychology so can't comment on it.
If you're considering any kind of biological science or materials science or even chemical engineering for uni, then chemistry is your best bet for keeping that option open. If you want to take psychology at uni, you do not need psychology at A-level.