If you could teach yourself for GCSE, with a little more effort, you can do the same for AS. It's a lot harder though. You need to have the resources though. Textbooks, revision guides, past papers, proper exam structures. If you need help with anything not in your books or anything, look online. You will get the help you need.
I spent about 2 months in year 12 at a sixth form and I hated it. I never really focused in class or understood most of the work so I always ended up having to teach myself, go over the context on my own so the transition to just teaching myself completely after I left, it wasn't that difficult.
I was nervous though. Only when I really thought about the consequences of not having an actuaI teacher/tutor. It was a scary transition from always having one to check my work. But with the help of textbooks and revision guides, I understood what I was doing.
You should constantly be doing practise papers to check your knowledge and practise how to answer the questions properly. I know that if I did this, I would've gotten better grades, especially in Psychology.
Psychology was my favourite subject, I absolutely loved it and I thought the two papers were my best out of all of my papers in the exams. I came out with a D, remarked to a C. I literally knew everything in the exam but my exam structure wasn't good. I wasn't answering the questions properly even though I knew the information. Now that I have started A2 Psychology, I've looked into better resources and I have seen books that focus on how to answer the exam questions specifically. I recommend you buy one of those along with the textbooks etc.
Also look into 'loopa psychology'. This guy has 12 mark question answers for all the topics in AS and A2. All you have to do is memorise them. He got A stars for both AS and A2 Psych. I wish I had used the templates.
You should be revising throughout the school year so you don't forget what your learn. You could make flashcards to help with your memory retention by trying to retrieve the information after you've learnt it. I use Quizlet. I've been using it since my GCSEs. It's a online flashcard maker thing.
I don't know how the process works for taking the exams with distance learning but I had to register at an exam centre as a private candidate. It was not cheap and the deadline to register for the exams is in February 2016 (if you're registering that way).
Good luck