I think taking 5 subjects is odd. Yes you might be able to handle it, but at the moment you have no concept of whether you will or not, and it will definitely negatively impact on your other 4, without giving you any real advantage. The best unis for Psychology want 3 As, so if you want to give yourself the best chance, I'd work hard at getting some sciences up to A grade. I've done a Psychology degree by the way, have worked with the admissions tutor for York at open days discussing what gets students in, and now work for the department. He just repeats 'the stronger the scientific background, the more chance of getting an offer' and obviously with thousands of applicants, most offers go to people with 3 As, even though the entry requirements are AAB/ABB.