The way A2 works is that they will have many different topics of a range of issues ranging from sleep to media psychology. Your teacher(s) will pick 3 topics for Unit 3 and again another 3 topics to cover for Unit 4 (Research methods is compulsory for everyone).
You must thoroughly learn the content in all topics because in the Unit 3 exam, they will test your recall of the knowledge by giving you an exam question which you must write an essay on based on the topic. You'll write roughly 3 essays (I'm just assuming that the questions are 24 marks each - they can split the questions up into two separate questions) in the space of 1 hour and 30 minutes - seems like a long time but when you're writing under pressure, that time is precious.
For Unit 4, again you must be able to write essays based on the topics you have chosen. You'll write roughly 2 essays (again just assuming that there are 2 questions that are both 24 marks) along with research methods at the end worth 35 marks. Statistics is involved but makes up a very small amount of the whole section. Most of the research methods that you learn at AS will be recapped again at A2. You learn the research methods in more detail (e.g. - for the 2 group designs (repeated measures and independent groups), they will have a stats test that you must use in order to correct find the correlation and significance for test results. Repeated measures design uses Wilcoxon T- test and Independent groups uses the Mann Whitney U-test).
My advise for A2 psychology is to start revising the topics early, that way you won't stress about how much you have to learn and cover before the June exams. Make sure that you truly understand the content on the pages and do revision notes/flashcards etc. to help you comprehend the topic. The most important thing to do at A2 is past papers, they'll help you get a good idea of how the exam will be set out and you can practice your essay writing with these too as well as research methods.
I do think you get into University by doing an A level in Psychology. It is possible! Good luck!