are the AS grades im hoping for realistic?

I'm doing my AS levels in maths biology chemistry and psychology. The truth is I wasn't trying much to begin with, I wasnt looking over notes or doing any work at home. I ended up with mock results in January of psychology-A, Maths-C, biology-U, chemistry-U. This was definitely a wake up call!! I then started revising more than I was, maybe an hour or 2 a night. On past papers im now averaging at psychology-A still, chemistry-B, maths-B, biology-C. I'm hoping for AABB in a months time, I'm not revising at least 4 hours a night, over Easter hols all I've done is revised and I have 2 hours with a private tutor as I have been since last month. Is it possible or should I be more realistic?