I was in the same position as you last year. As EPL.11.4ever has said, it is definitely achievable. However, you do require large amounts of practice and concentration if you want to do well. In my opinion, you do not need any Units 1&2 at all as everything is re-taught.
As long as you pay the subject respect by practicing and concentrating, you can do well. It is not a hard subject
I'd agree with that. As far as I know, the basis and foundations of Units 1/2 Accounting are gone over in Units 3/4. There are two main bits to Accounting;
theory and
practical.
If you break it down, Accounting is a subject which is easy to do well in.
The practical is quite easy as you'll do the same exercises over and over again, so you'll get it eventually even if you're unsure at first. The practical is easy in that sense. The questions in textbook and exams etc are pretty much the same, they are just worded differently in some cases. You can learn some "textbook" responses to certain theory questions which can gain you full marks.
Practice is essiential if you want to do well in Accounting, this can be done through exercises in the textbook and practice exam papers. The more you practice, the better you'll get at Accounting.