Apart from English, the maximum number of marks I have lost on SACs is 5.
I think it is just practice. Do Checkpoints, A+ notes, A+ exams etc before SACs for the particular topic being tested as it really helps you eliminate mistakes on the actual SAC. Try and do as many questions as possible.
Chemistry is my only subject, other than English, that I am utterly displeased with. This is because I could probably have done slightly better, perhaps 45-46 if I hadn't got so stressed during the midyear exam. Controlling anxiety is very important, as if you are overly anxious on the day, you'll have trouble thinking and mistakes are easier to make. Maybe this explains why I came so close to 50 in three of my subjects

When studying - for subjects like Psychology in your case, read the theory very carefully. Preferably twice or more, as the small details really need to stick.
Good luck!