There's a significant amount of content involved, however I wouldn't say it's particularly difficult. There's a lot of stuff to remember but it's enjoyable and very interesting. Having said that, no offence, but looking at your grades in the core subjects I'm not sure how you'd cope. What exam board is Psychology a level on at your school? The scientific content isn't immense, but there is an entire chapter dedicated to biopsychology which requires you to have knowledge of the nervous system,brain structure, endocrine system etc.. It's nothing compared to A level biology but can prove challenging to someone who struggles with science. The maths involved are quite basic,and regarding English, as long as you're able to write effective essays and communicate the points well you'll be fine.
What do you want to study at uni?